This started as a short post with a few bits of advice, but I got carried away... Anyway, not knowing what exactly you have problems with, this is my list of general advice for staying alive, most of which you may already know.
1. Prioritize inscription slots over unlocking new categories. You should look to get a 4th inscription slot as soon as possible, unless the tree that you are unlocking substitutes for a good inscription (very few trees would qualify in my mind, but celestial/light is a good example). One advantage to playing a cornac is that you can have 5 infusions at level 10, which should make it much easier to survive.
Be sure to visit all inscription/charm shops you can and shop around for what you need.
2. When it comes to inscriptions, prioritize those that let you escape over those that let you stay in the fight. A combination of movement infusion and teleport can get you out of any situation. If teleport is unavailable to you due to being antimagic, get another movement infusion but try to find some way to escape surrounds - psychoportation charm, dream walk (from escort), telekinetic leap (from wanderer's rest), etc.
Movement is better than teleport, because uncontrolled teleport is a gamble - you are gambling that the tile you teleport to is safer than the one you are standing on. In any case, running away when you are insecure if you can handle the situation is safer than using it as an "Oh Shit" button - but that comes with practice.
3. Prioritize defensive and escape abilities over offense, prioritize defensive stats (especially status resists) on gear. Doing crap damage and having 50% stun resist is superior to doing good bursts of damage with 0% resist. This is a game of long term survival, not flashy numbers.
Learn to packrat. Save all +stat gear (for non-primary stats), in order to qualify for items and prodigies. Save gear that gives elemental resists and learn to change gear sets before dungeons. Lightning resist is particularly useful in the early game, and fire and blight resists stay very useful for the whole game.
Until you get your fortress, you can use any vault or the ruined dungeon to store your loot.
4. Learn to handle status effects.
Stun is a major killer in the early game. If you get stunned, clear it with a wild infusion and look to escape until your wild infusion comes off cooldown. If you can't clear it off, trying to walk behind a corner with a movement speed penalty is still better than staying in place and fighting. Psychoportation charms cannot be put on cooldown by stun which can make them a superior choice to teleportation in some cases.
Confusion can be walked off most of the time. Pop a movement infusion and walk out of LOS. Since instant abilities cannot fail due to confusion, this is an almost foolproof way to handle it, as long as you have space to run to.
Blind can also be walked off, as long as you were paying attention and can walk away from memory. If you aren't sure, switch movement mode to passive in order to not bump-break your move infusion. Wilds are notoriously unreliable for handling blind, so don't rely on it.
Those are the three major ones, apart from poisons and diseases, that you will have to learn to handle in order to at least get through Dreadfell.
5. Don't be lazy.
Auto-casting and auto-explore speed up play, which has good and bad sides. The positives are obvious, but on the minus side it gets you in the habit of not thinking about your surroundings and tactical situation. If you play the game like 1,1,z,1,1,z,1,1,z you will get into the habit of just thinking about getting through the next mob, and not about how what you are fighting can kill you. So when you get through 90% of the trash mobs that make up a typical level and meet a tough mob, you will likely make a rash decision because you are simply not in the habit of thinking about how best to handle the situation, just how to remove the roadblock that stands in your way.
So play patiently and learn to make the right decisions first, and then speed up your game when you get comfortable.
6. Don't reinvent the wheel.
Everyone likes to play something original that no one has done before, or at least something that people don't usually play. If you are still coming to grips with the game, look through winners on te4.org and how those characters were built, and then think about the order in which it would be best to learn those abilities. I used to fully plan my 1-50 build (apart from random stuff like alchemists) on a sheet of paper, but that might be too much work for a game.
There is also an addon that helps you do that.
7. Learn positioning.
Death dance, Whirlwind? Forget about it. You don't want to be standing surrounded by melee mobs. If you are fighting more than one at a time you are probably doing it wrong. Don't fight in open spaces, reposition yourself in a hallway. If you don't have a good hallway for fighting, dig one.
If you don't know what the mob does, inspect it. If you are still not sure what it does, run away from it.
8. Handling casters.
I could probably write a whole post about this, but the gist of it is that you want to isolate the caster and neutralize it if possible (stun works great here because of the low number of abilities npcs usually have). Nasty sustains like Bone Shield and Essence of Speed are a good sign that the mob is too dangerous to fight, even if you can dispel it.
9. You don't have to kill everything.
No, you really don't. At some point you will probably find something that you will not be able to. The Ancient Lich boss in Slime Tunnels (spoiler alert) hammered this point into the coffin of a few of my characters. If it really bothers you so much, make a mental note and come back later when you are stronger.
A short list of things you especially don't want to fight if you don't have to:
Horrors.
10. Avoid death traps.
Entering the bottom of lake of Nur on level 18 is fine, but there is no need to go up against the hardest enemies in the game (horrors) that early. Pop in to keep them at a reasonable level, then go do something else. Packs of luminous horrors are great for killing characters, so don't give them the opportunity that early.
Don't open vaults unless you have a plan on how to GTFO if things go wrong. Clear the whole level, dig yourself a zig-zag escape tunnel near the vault entrance if necessary, just don't go opening it too early and unprepared. The same goes for chests.
Don't do the dark crypt until you can beat the Master comfortably. Don't do Mark of the Spellblaze until you can dispel Fearscape. Don't do Last Hope graveyard until you feel comfortable handling any kind of rare the game can throw at you. I usually wait past level 30, unless I'm going for lichdom.
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Hope that helps.