[DarkRanger]

To add; heavy armor and shield=guardian(exception for cleric usually), no shield even if wearing heavy armor=flanker(possible exception for certain monks)
-not every attack should be a knockdown attempt. Use it once when melee hasn't started and you can easily target the enemy on the other side of the room, but after the fight starts leave that button alone, especially when there's more than one other PC meleeing, and/or the enemy is small/flying. If you're the only one in melee you could use more discretion but keep in mind it reduces your chance to hit.


Advanced tactics-
Casters should be first target. Good AC guardians should try to pass close by melee enemies on the way to the casters to draw their attention if possible, but be sure to take out any casters. If a caster joins a fight in progress, either by rising undead or entering a door, they become top priority.

After taking out the enemy's casters, try to prioritize your targets as follows;
hit any heavily damaged enemy first
next heavily damaged
leave stunned/turned/dazed/etc enemies alone unless they're near death

Best place for cleric is between the melee and the casters, to take attention off casters or rush into fray to heal. Smaller, higher level groups, with clerics of certain builds, can use them as the frontline or part of it, but generally they belong in the middle.

If you can't avoid a wide level range, it's better for melee to be higher than casters. A level 10 wizard can still throw missiles at a level 15 fighters spawns, but a level 10 fighter can't hold a level 15 wizard's spawns.