Bluffing question

In my constant pursuit to improve my game I have notice that I do not bluff often enough or when I do bluff it is often at the wrong times. This got me thinking about how I need to improve on this part of my game. So, my question is excluding stealing blinds shorthanded in a game, what is it that you look for in determining whether or not to try a bluff? What does it take for you to give up on a bluff?