Warning: Don't read this if you don't want to know some of the secrets of the game.
Play through with the warrior first.
Don't fight monsters if you can run away. You don't get anything for defeating them... Extreme caution helps you live. Slimey cubes are very dangerous, even when you are stronger. Don't fight them without arrows or magic items.
If a monster can't swim, go across the water, and shoot arrows at it.
If in a corridor (or similar situation), with a weak monster next to you, and a stronger one behind it, shoot arrows at the stronger one before attacking the one close to you, unless you would die from that strategy. Like snakes and wyrms is a good time to consider this.
Maps and hourglasses help a lot to stop you from dying.
Some monsters can't open doors, so you can escape behind one (if you freeze time), and shut it.
You can shoot arrows through a closed portcullis.
Go up and down levels a lot.
Go up and down the first three levels for a while.
Don't go down too fast!!!! Except, if you have a recall stone, then go down as fast as you can, and use the stone to escape too dangerous situations.
Push boulders up against monsters trapped behind them. Either, the monster will be crushed, and you don't have to take the chance of fighting them, or the boulder will get crushed and there is a chance that you will find an item inside the boulder. That item could be from any level in the tomb. You can also push some monsters back if they are behind a boulder with a corridor behind them. You can't trap/push/etc any ethereal monster [ghosts and wraiths] with a boulder.
Your first goal should be to get down to level 7, and get the first unique item, in the special chest. (the chest shows up on different levels for different hero types) If you can, find the altar on each level on the way down. (It shows up on a lower level each time after you find it, but only the first 7 times, then its random.)
Your next goal should be the second unique item, which is somewhere in the mid levels.
Your last goal should be to build up to defeating Angelus. Collect lots of swords (some classes can't get swords, and would get slightly different items to fight Angelus), books, hourglasses, wards, a charm or two, and a map, and find the altar a lot. You can't defeat Angelus without magic items (unless you build up for about 25000 turns...) Angelus will also shoot arrows at you if you are in range, or summon monsters if you are not, so you never never want to be on his level without ward or hourglass active.
Even with good playing, you might only win 1 in 10 times... (That is my average rate so far)
Good Luck!
Angelus the Necromancer
(c) 2005 Jim DuBois