Always be aware of how many players are in the hand. If you’re thinking of bluffing with four or more people in the hand, think again. Unless you’re trying to scare out a few players to protect your hand, you should restrict the majority of your bluffs to hands involving three or fewer players. Any more than that and you’ll typically get an “I’ll keep you honest call” which are words you never want to hear while your bluffing.
Be sure you are in a situation to bluff. Hold’em is really a game of position. If your opponent has by now checked, you are in a little better position to bluff. If a strong player checks to you, watch out for a trap or re-raise. There’s naught worse than trying a bluff and getting check-raised.
Know the table well. Before trying to bluff anyone you must have a good idea of the types of players you’re up against. Keep your bluffs aimed at middling players. If they are awful, they’ll call no matter what. If they are great ones, they are more likely to call for future reference so as to get a read on how you play.
A semi-bluff is always better than a full bluff. You must consider bluffing with a draw or just a mediocre hand. That way if your bluff does not drive out your opponent, you still have a possibility to make your hand and win the pot. Most of your bluffs should not be true bluffs. They ought to be semi-bluffs.
Don’t bluff overmuch. People who overbluff get calls they usually wouldn’t. This is fine if you have the best hand, excluding cases when you’re just barely ahead or someone is on a draw, being labeled a regular bluffer will just give other players an excuse to call and outdraw you with hands they would on the whole lay down.