Only tip I have is to make sure it's a believable story. Most bluffs are set up well in advance and make sense in the context of the game and players.
This is the perfect advice. A bluff is about your story so you have to think about what story you have been telling. What is your table image? How have you been betting in certain situations. How does this situation compare to those? Have you been showing down strong hands or have you been caught in a bluff lately? In addition, you must have good reads on the other players. Some people will scream position, position, position, but would you rather be bluffing into a couple of super tight players out of position or a calling station in position? So, your reads on the other players are critical. Finally, examine the situation, if you are bluffing into a 9 6 2 rainbow flop, what are you trying to convince your opponents that you have? A pocket pair that hit a set, maybe an over-pair, maybe 78 suited. Did you play the hand you want them to think you have?
One last point is that it does matter what your playing and where your at in the game. Bluffing is much more difficult in freeroll and microstakes tourneys, especially early, it can also be pretty difficult when your playing small stake ring games or during the re-buy period in a lot of tournaments.
With all of this said, bluffing is essential to playing good poker and it is a skill worth learning.