Reward, Don't Punish
Ever feel the need to "correct" certain player behavior?Maybe the bard doesn't keep in character. Maybe the rogue hordes all the loot to herself. Maybe the fighter is consistently late for your sessions.
As DM, you hold all the cards in-game. It's easy to go on a power trip and and bully your players into "proper behavior" by deducting XP, stealing their loot, humiliating or crippling their characters, or any other punishment the creative, evil genius of a DM can imagine.
Whatever the undesired behavior is, punishment is not the answer. D&D is a form of entertainment -- it is a game, not an elementary school class. Punishing players is a childish way of dealing with a problem, and your players -- who are probably your friends -- aren't gaming with you so they could be scolded and reprimanded.
As DM, you must have the courage to be honest with your players about what you expect from them, rather than enact revenge upon those who do not conform to your desires. "Well-behaved" players may feel uncomfortable seeing other players punished and leave your game for one with a friendlier atmosphere.
If a certain player refuses to play by your rules and is ruining the fun for the other players, then you should take him aside and have a frank discussion about the issue. He can clean up his act or find another gaming group.
The best way to encourage players to behave a certain way is with the carrot, not the stick. Instead of punishing "bad" behavior, reward "good" behavior. The D&D game is constructed to reward only combat and dice-rolling. If you award bonus XP for good roleplaying, clever planning, creative use of spells/equipment, or whatever type of behavior you'd like to see your players engage in, then you'd be surprised to see the effort your players will put into gaining those rewards. The carrot doesn't even have to be XP -- use your creative genius to come up with an interesting reward system.
Always remember -- it's a game. The goal is to have fun.
