This thread has a lot of great survival tips, although most of them are more strategy based than stat based. I especially recommend reading Thomas, Pigslayer, and my posts in that thread. As for building your character for defense, you'll definitely want a good Infusion setup. My general recommendation is Movement, Heroism, Wild (physical/mental or physical/magical), and Regeneration on almost every character, and either another Movement, Heroism, or Shielding for the last one. Some classes such as Corruptor, Marauder, and Archmage have very different optimal setups than this so this doesn't work for every class, but it's optimal for about 70% of classes. As for defensive stats, I'll list them in the order of importance.
1. Stun and confusion resistance: These two statuses can completely debilitate you and should be avoided as much as possible.
2. Health: Resistances can't protect you against everything. Lots of health will often give you at least enough time to get out of a bad situation.
3. Damage resistances, especially physical, fire, cold, blight, nature, and mind: Although high level Orcs get very high resistance penetration, most enemies early and many late (like Demons, Horrors, and Dragons) do not. 70% cold resistance can turn a 1,000 damage freeze into a 300 damage freeze, which does wonders for your survivability. Hold onto resistance rings and switch them depending on the zone, for instance, lightning in Tempest Peak, fire in the Charred Scar, blight in the Dark Crypt and Rak'Shor Pride, fire and cold in Vor Pride and Armory, nature in the Sludgenest, etc.
4. Healmod: If you have 50% healmod, your Regeneration Infusions and healing talents are that much better. Try to stack large amounts of this once you've eliminated the possibility of being instakilled.
5. Other status resistances, especially disease, poison, and pin: This prevents you from wasting your Wild Infusions on lesser statuses when you're stunned as well. Diseases can be very deadly and poisons, while weaker, cause annoying effects like reduced damage, talent failure, and immobilize, and pin can mess you up if you need to escape making them the next most important resistances after stun and confusion.
6. Critical reduction: Really hard to get at the moment since the only sources are Dexterity, Armor Training, and Indiscernible Anatomy, but this is seriously good. I think some items with this stat are being added next patch and Brawler is getting a good source of this too.
7. Armor and armor hardiness: Makes melee much less threatening. Amazing early, not as great late but still decent.
8. Saves: These aren't reliable enough to warrant skipping a Wild Infusion, so don't bother stacking these. Physical save is probably the least bad of the three, but spell save is pretty much worthless.
9. See stealth/invisible: Good against guys like Orc Grand Master Assassins, but getting these to decent levels is futile on higher difficulties. Probably more important than mind and spell saves on Normal.