Basic "Keep alive" tactics:
1.Always read the automap! Press TAB while in a dungeon to find your way to the nearest unclear area of monsters or exit to the level (if you have hellfire, try to find a WARP book so you can get to the exit with ease).

2. If you ever find yourself in a room of BIG monsters and you can't take them all at once, chase them into a doorway or narrow hallway where only 1 or two monsters can fit. Then they can't gang up on you, and you pick them off without tons of trouble. NOTE: Do not stay INSIDE the doorway but directly outside of it, within a sword swing of the inside of the doorway.

3. If at all possible, try to avoid using two handed weapons on level 15 and 16, Because of all the amounts of soul burners, advocates, and blood knights, a good shield is essential to survival.

4. If you ever find an item that has FASTEST HIT RECOVERY (of harmony suffix) pick it up and try to find someplace to use it without taking away an item of much greater power, before going down to hell or confronting large groups of Storms, spitters (especially lava maws), and succubi. The reason I say this is because when you get hit by either of these monsters without enough experience (lvl 23 in normal, 27-28 in nightmare, 32 in hell) you will get hit and not be able to move for about 1 second, but if the flow of hits keeps hitting you you can't recover and they will have you trapped for an easy kill.