http://te4.org/wiki/classes-archer
Updated for 1.25
Goals:
You want to move, shoot and especially kill faster than your opponents. You want to shoot faster than your shadow, loosing 10 shots where other loose 1. You want to exact biblical punishments on your enemies.
Racial Choices:
Cornac – 5/5
Contrary to what I wrote when I first posted this guide, Cornacs are now an excellent option for any archer. There are several worthwhile locked categories, and Stone Alchemy is an interesting option as well. You will have generics to spare though, so pick up either Stone Alchemy or Antimagic.
Higher – 2/5
The sight range is nice, but you won't have the willpower for the scaling regen, the stats are rather uninspiring, and you won't have stamina problems. So - no.
Shalore – 5/5
That's what I went with. The first talent, Grace of the Eternal, is amazing, especially coupled with your insane attack speed. 10% Crit from the second talent are superb as well. Timeless sustains your speed boosts, and more importantly, gets rid of status effects, which you'll have a lot of due to relatively bad saves. It also resets the cooldown of your skills and runes, which is invaluable as well. The low hp are certainly a drawback, but one you can (hopefully) live with.
Thalore – 4/5
You won't have any willpower to let their talents scale, but they're still great, especially the disease immunity and resistances, which will help a lot with the final fight (which pretty much should be your only real hurdle past the early mid game). They might even be 5/5 - I'd have to try them.
Halfling – 3+/5
You'll be critting pretty much always anyway, so Luck of the Little Folk is mainly a bonus to saves. You don't really need evasion, since you won't spend much time getting hit by physical attacks. Getting rid of stuns and the additional saves and HP are nice, though. The starting stats are perfect as well.
Dwarf – 1/5
Power is money is, obviously, very nice. Apart from that, only Stone Walk really shines, making Dwarves a less than optimal choice.
Yeek – 2/5
The global speed is plain brilliant. Everything else - not so much. And we really don't want to be THAT squishy.
Skeleton – 3/5
The racials are nice, though more suited for a bow-using archer. Still a decent choice, I guess. The shield is amazing on a dex-based class.
Ghoul – 0/5
Errr, no? You want speed, they have a speed penalty. 'nough said.
Attributes:
For maximum fun: Dexterity and Cunning until they are both maxed out, then constitution until you max Thick Hide. You want and need the damage and the crit rate. You might even want to get some Strength in the end to further boost your damage through physical power.
You might start on constitution a bit earlier, though, and keep Con-boosting items to get Thick Hide earlier.
Class skills:
Archery-Bows (class, 1.3 mastery)
You're using a sling. Zero points here.
Archery-Slings (class, 1.3 mastery)
Sling Mastery - 5/5
Eye Shot - 1/5 or more
Inertia Shot - 1/5
Multishot - 0/5 or 5/5
Sling Mastery is your most important skill. Period. It boosts all your damage.
Eye Shot is brilliant. Get it early, use it a lot, improve it when you have spare points.
Inertia Shot is nice, but works fine with just one point.
Multishot's damage can be nice, but it costs a lot of stamina, requires a few points to be effective (which you won't have until late game), and (as far as I can tell) hits only 3 times despite claiming to hit 4 times. With that said, it is great for removing bone shields, applying poison and weapon-based debuffs and does a nice bit of damage.
Archery Training (class, 1.3 mastery)
Steady Shot - 3/5 or more
Aim - 1/5
Rapid Shot - 5/5
Relaxed Shot - 1/5 or more
Steady shot is your main attack skill. It has a low cooldown and does a lot of damage. You will probably want to max it at some point.
Aim and Rapid Shot are mutually exclusive, and you're going for Rapid Shot.
Rapid Shot is just brilliant. Sure, you do lose quite a bit of damage, but the attack speed makes up for it. Believe me.
Relaxed Shot can be delayed until you start experiencing stamina problems in longer fights (that is, until you start having longer fights

Archery Prowess (class, 1.3 mastery)
Flare - 1/5 or 3/5
Crippling Shot - 3/5
Pinning Shot - 1/5 or more
Scatter Shot - 5/5
They're all brilliant. A few explanations: Flare damages only your main target, but blinds in an area starting at level 3. Which is why I suggest investing at least the extra two points to get to that level.
Crippling Shot is amazing. The slow works on everything including bosses, and with a 40% global slow, Grace of the Eternal (or Blinding Speed) and Rapid Shot, you're getting out 6-7 shots for every action of theirs. 3/5 is enough though, since Crippling shot is capped at 40% and scales with Accuracy, making you reach that 40% with a mere 3 points. Eventually, 2/5 might be enough, but it is a pain in the ass to keep that one point floating indefinitely.
Pinning Shot trivialises melee bosses. You might get by with one point, though, considering those 2 turns of pinned are ±8 shots for you, and you still have inertia shot. If not, invest some more points.
Scatter Shot is your only area attack, and is brilliant. It uses smite-targeting (that is, the "projectile" always hits the target square regardless of any enemies it might encounter on the way), hits whole vault rooms and stuns. What more could you want?
Combat Techniques (class, 0.9 mastery, locked)
Rush - 1/5
Precise Strikes - 5/5
Perfect Strike - 1/5 or more
Blinding Speed - 5/5
Leave Rush to those who can't handle a sling.
Precise Strikes is very nice. Sure, it decreases your attack speed somewhat, but it adds a lot of crit and accuracy.
You won't usually need Perfect Strike, but might want to use it if you encounter rares combining, say, Shield Wall and Setup.
Blinding Speed is absolutely essential for this build on everything but Shalore. 40% global speed on demand, without using a turn? What's not to like?
If you are a Shalore, you might as well skip it.
Poisons (class, 1.2 mastery, locked)
Vile Poisons - 5/5
Venomous Strike - 1/5 or more
Empower Poisons - 0/5 or more
Toxic Death - 0/5 or 3/5 or more
Vile Poisons are nice. 30% damage reduction? 30% talent fail chance? I'll take those, thank you very much. Venomous Strike is simply one more attack with a decent damage multiplier; it also does nature damage, which can be useful in some cases. Empower Poisons seems nice and is instant use, but you will rarely need that poison damage to secure a kill. Toxic Death could be fun to get, I suppose, but you apply poisons so fast it hardly seems necessary.
Archery Excellence (class, 1.3 mastery, locked)
Shoot Down - 0/5 (or 2/5)
Bull Shot - 0/5 or 1/5
Intuitive Shots - 0/5 or more
Strangling Shot - 0/5 or 1/5
Shoot Down is amazing, but I do not think it is needed here. You can easily dodge many projectiles as long as you have any missile speed decrease, simply because you will get 4 or 5 actions per round.
Bull Shot looks nice, but you do not usually want to charge anywhere; you want to stay back in safe terrain and let the enemy come. Intuitive shots looks great until you realise you will not be hanging around in melee in the first place. Melee opponents really aren't that much of a problem, either.
Strangling shot offers silence, which is always great - but again, you probably will not need it. Any opponents you get to shoot at will be stunned, slowed, slowed more, weakened, crippled and blinded. When those effects run out, they will be dead. If not, use timeless and repeat, or teleport out. A silence on top of that is just showy.
Combat Veteran (class, 0.9 mastery)
Quick Recovery - 0/5 or 1/5
Fast Metabolism - 0/5 or 1/5
Spell Shield - 0/5 or spare points
Unending Frenzy - 0/5
I suggest ignoring Combat Veteran unless you find yourself with points to spare (which is quite possible, really).
Dirty Fighting (class, 1.0 mastery, locked)
Dirty Fighting - 0/5
Backstab - 0/5
Switch Place - 0/5
Cripple - 0/5
Ignore the tree. Why exactly do archers get it in the first place?
Generics:
Field Control (generic, 1.0 mastery)
Disengage - 1/5 or more
Track - 1/5 or more
Heave - 1/5 or more
Slow Motion - 0/5 or more
All good skills for this build, really. Get Slow Motion for matrix-style missile dodging. It's actually pretty good. Disengage and Heave will save your life. I left them at 1, though. Track is useful if enemies blink around corners or you get fearscaped, or to scout out dangerous areas.
Combat Training (generic, 1.3 mastery)
Thick Skin - 5/5
Armour Training - 5/5
Combat Accuracy - 5/5
Weapons Mastery - 0/5
Dagger Mastery - 0/5
Thick Skin should be maxed on pretty much every character. You can comfortably delay Armour Training, but you will want to have it by the time you reach High Peak, if only for the Crit reduction.
Survival (generic, 1.0 mastery)
Heightened Senses - 5/5 or less
Charm Mastery - 1/5
Piercing Sight - 1/5
Evasion - 0/5 or more
You should always be able to see enemies the moment they come into sling range, if not earlier. Heightened Senses does that for you. Piercing Sight is fine at just one point. I never got Evasion, you might if you find yourself in melee more often.
Escorts:
Thieves are basically free generic points. Use those to get piercing sight, if you can, especially if you don't plan on getting Evasion.
Warriors Get Vitality, I guess, it might even save your ass.
Temporal Explorers are more or less useless for you.
Alchemists are actually nice - you do have the generics to spare, so get Gem Magic if you are a Cornac. If not, stick with Dexterity.
Anorithils offer Cunning, mainly. Light is nice, but you wont' have much in the magic department.
Paladins are nice for Chant of Fortitude, which is great, or Chant of Fortress (which is very nice for archers as well).
Get Premonition from Seers. It's fantastic.
As for Sages, they offer a nice +2 to dex or cunning, which is not too shabby, really.
Infusions:
Shielding, Shielding/Heroism, Regeneration, Physical Wild, Teleportation
Get a teleportation rune as fast as possible. For you, going away, then coming back from another angle and with a lot of distance between yourself and your enemies is almost always the best approach to sticky situations. And due to your high speed and decent mobility, you can usually handle whatever you teleport into.
The physical wild can also be exchanged for a movement infusion, as the latter can handle stuns and pins better; however, you then lack an option to get rid of disarms, which can be very nasty as well (though most of those are applied in melee, so if you feel you can avoid them, stick with a movement infusion for the early game at least).
Shielding runes don't blow turns and effectively give you a larger hp pool when popped at full health (thus helping to prevent instagib), so they're perfect for this build. A heroism infusion goes well with that if you manage to find a decent one, offering both a nice damage increase and amazing survivability. If not, get a second shield rune.
You will want a second (mental) Wild infusion until you get Timeless. You won't need it though after you get to the east and get Relentless Pursuit.
Prodigies:
Vital Shot.

It's very, very good, especially coupled with Crippling Shot. Those two combined make a shootout hilarious - you'll get off something like 13-16 shots for every one of theirs. It also one-hits a lot of enemies, especially mage types.
Elemental Surge might be nice if you have a sling with damage conversions.
Crafty Hands is a must if you got Alchemy.
If you don't go Shaloren, you might consider going Antimagic and get Windtouched Speed.
You can also consider any of the defensive prodigies, or Fast Hands, which allows you to get by without a teleportation rune, since you can switch in a teleportation torque or amulet whenever you need it, as well as enabling you to switch ammo on the fly to apply different debuffs to an enemy.
Equipment:
Look for Global Speed, Movement Speed, Critical Hit Chance, Critical Multiplier and Damage. Flat HP bonuses are great early on, but less important later on as you slowly get a decent amount of HP yourself. In the late game, Physical Resistance Penetration becomes comparatively more important and should get priority over most other stats. Resistances to common elements are also generally useful and not to be underestimated.
You'll probably want to wear a dagger with nice "when wielded/worn"-stats in your offhand. You might also consider wearing a shield if you find a really good one, just for the defensive stats it might offer. Don't bother blocking, though.
As for your weapon, a high range is very important. Apart from that, look for the same abilities you'd want on your shots. As for your shots, their most important feature is their base damage, followed by a large ammo capacity and useful on-hit or on-crit abilities (since you will be hitting and critting a lot, making 20% chances really, really huge). Prime examples for the latter include crippling, insanity and slowing effects.
One other attribute is not to be underestimated: missile speed. This can make the difference between killing a mage before he gets his spell off or not, and can prevent you being pulled into your own shots as well.
During the lategame, preferably before doing Vor Pride, you should start stacking resists, and preferably get immune to stuns before the final fight.
Skill order:
Get your active skills to at least 1, Crippling Shot to 3 and Sling Mastery to 5 before you start maxing rapid shot. Spend an early point in aim, though, since it's really strong in the first few dungeons to toggle when shooting at, say, an advancing Bill.
Spend your first category point on Stone Alchemy if you are getting it, else use it for an inscription. Poisons are very, very useful throughout the game for their debuffing effects, so you might consider getting those with your second point, followed by Combat Techniques. I do not think Excellence is needed for this build (even though it seems useful), so I suggest skipping it for now.
Early game advice:
If you started out as a Shalore, here are a few hints to survive the first dungeon.
1. Whenever you see a crystal, pop your shield and Grace of the Eternals.
2. You can dodge their projectiles. Do it.
3. Heal after every fight.
4. As for the boss, try to flee when you get low, heal up and come back. That's what your phase door rune is for.
In general, elemental damage on shots or weapon is very strong early on (most other elemental damage is melee only, unfortunately).
How to play:
Use and abuse your speed. Whenever something looks dangerous, pop heroism (if you have one) and a speed buff (and possibly a shield), fire a Vital Shot, cripple it and/or pin it if its a close-range fighter, maybe blind it for good measure, and start the biblical punishments.
Against multiple enemies, pop heroism, the speed buff and shield, stun them, and alternate standard shots and Steady Shot until everything is dead, using Vital Shot, Pinning Shot and your other tricks to handle individual threats.
When a projectile approaches, dodge it. When someone gets into melee range, disengage or heave unless you can kill it quickly.
When things get rough, teleport.
Problems:
There are a few things that can really spoil the fun:
1. Lots of bad status effects. (usually not so bad, unless they come from enemies that also take ages to kill, like the final bosses, so Timeless and Relentless Pursuit will be on cooldown when they stun you yet again).
If you go for gems, you might consider gemming for stun immunity.
2. Shadows and people that summon them. They can kill you fast. Kill them faster. If you have more than one shadow adjacent, port away.
3. Instant casts. Those can really ruin your day, since you ARE relatively squishy and sort of rely on your enemies not getting out more than one spell at a time (and usually not more than one spell at all, if that). Pop a shield if you expect instant casts. Actually, just pop a shield at the start of every fight if you can.
4. Pulls and swaps. Being pulled or swapped into your own vital shot will one-shot you. Every time. Bladed Horrors (quite common in Lake Nur) are one opponent that likes to pull you into them; take care that you only shoot them from outside of their pull range (which is 5, I think), or after they pulled and you disengaged (so they'll have cooldown).
Pay special attention to the pesky mages in the Crypt as well (if you enter it at all!), they like to swap you around.
5. Overconfidence. You will kill most opponents without breaking a sweat, including most bosses and the pride entrances. Don't get cocky. You will in all likelyhood be comparably squishy. Play accordingly.
I guess that's it for now. Thanks to Jenx for his comments. Further suggestions and criticism are, of course, very welcome.