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Edit) Post was longer then I thought. Maybe you can make do with a summary at the bottom!
The most important thing to do (and this really applies to all roguelikes, more or less) is to secure an escape route incase defeat becomes a possibility, and to never get surrounded.
This one hint could be considered cheating, but it's more like exploiting game mechanics: Say you enter a cave to kill your quest monster. I am Lokum Stabsyouintheface! Prepare to die! And all that: As long as your speed is at least 1000, lure your target enemy up and out of the caves and all the way to the edge of the map. Make sure you're right on the edge, then attempt to fight. As soon as things get bad (a broken leg? Massive damage?) leave the map. It's as simple as that!
Two, beware of groups. One skeleton is pathetic. Three can knock you down and break your legs. One snakeman isn't too dangerous; but a couple and your chances to get paralyzed are MUCH higher.
Next, be on alert for tough enemies. Mud men are never very tough, but giant toads can cause some serious pain. Cave crocodiles are EXTREMELY dangerous when you're weak. Anything that has a ranged attack is extremely dangerous no matter how strong you are. Snakemen can bite and paralyze you. Everything hurts more when you're knocked over: don't get knocked over, unless you're one move away from leaving the map. Even then, it's bad. When you're knocked over, Mud Men can bruise and break you, and they'll often attack three times to your one. A cave crocodile doesn't even need that much time to kill you if you have poor armor and skill.
Beware of encounters in the wilderness. I've lost a few adventurers due to being lazy and holding a direction only to keep running into a tree while a lion surgically removes my limbs. If you feel brave enough to attack your attackers, stay near the edge of the map. Be sure you can escape. Start off with ranged attacks: a broken arm or leg from a rock can turn a hard enemy into a matter you don't even need to concern yourself with, although prone enemies don't offer any skill.
Almost Lastly, be fast. The most dangerous aspect of being knocked over is having about 1/3 your normal speed. Weak characters with little agility will become burdened: keep your speed at or above 1000, or only slightly under and be ready to drop something to make a run for it. You can't out run anything with 900 speed. Even characters with 1818 speed are in serious trouble when they fall down! And they WILL fall down.
My final bit of advice is to always keep cover around if you can. Marksmen can kill you if you can't get out of their line of sight in one or two moves. When you do, either make a run for it or sneak and hide. Don't try to close distance if the marksman is any respectable distance away: I'm thinking two moves is the maximum you'll want to try, UNLESS they can't see you and don't know you're there! Don't try to beat marksman from a large distance with rocks; you probably can't hit them unless you're close enough to move up and smash them in melee.
Remember that anything, anything has the chance to kill you in the right conditions, just as you essentially have the chance to kill anything if you're lucky. If it works for you once, congratulations. If it works for them once, it's game over. A lowly harpy, all alone, managed to move to my heavily armed and armored, fully healthy warrior and in one hit broke through his armor and piereced his heart. He died from bleeding one turn later. It's rare: but it's possible.
Summary: Always be ready to run. Don't get knocked down. Don't take on anything you can't handle for sure. Always be fast: at least 1000 speed. Don't get outnumbered or surrounded. Anything with a ranged attack will kill you unless you're right next to them and have a sharp object in their brain.
...Don't flood the fortress you're exploring while you're still in it. =)
[ May 22, 2007: Message edited by: Keiseth ]