After constantly dying in ridiculous way you begin to pick up on certain survival techniques, and methods/steps to take to avoid death. Sometimes death is inevitable due to RNG, terrible circumstances, or terrible decisions made before the "I'm DOOOOMED" moment.
A major survival technique is stair dancing. Be smart about it, always know how far away you are from a secure up/down staircase. If you run into a room full of orcs for example, and your character is still early, run towards the nearest staircase and bring a single orc with you. Take him out, rest, and either fish up some more orcs or find a different way to reenter that level. Bringing up more baddies may be a really bad idea depending on how narrow the "safe" side is, and how many things are surrounding the "unsafe" side. Never engage orc hunting parties unless you know that you can take out the priest quickly. The longer you're in their vision range the more likely you are to die. Remember to learn from each and every one of your deaths, if you have to write down notes then do it. And don't be afraid to skip entire d-levels if things are too hot, like a roaming sigmund/grinder, or some ogres which you can't handle. Or a ghost.
Speaking of orc priests.. I just lost my level 15 Fighter to a single orc priest due to stupidity. I simply refused to quaff my last heal wounds potion while I swung at him, and he ended up smiting away the last few hitpoints. It would have helped if I checked what armor he was wearing, that was probably why I didn't kill him quickly enough. Had some good Okawaru gear too.. oh well.