Problem: Enemy has high AC and you're a fighter sort
Solution: Touch attacks. Impaling Weapon and Martial Study: Emerald Razor are two good ways, plus gaining access to the ever-popular Wraithstrike.


Problem: Nothing you do can hurt the enemy directly.
Solutions: Target their environment, take steps to make them waste their actions, or help your allies (including "Aid Another" if necessary).


Problem: You want to play a monk
Solution: Play a Tashalatora PsiWar, or an Unarmed Swordsage.