The better question is "when" not how often. Like many have said before me, it depends on the flop, position, villain (s), table image and your hand. Don't feel like you have to c-bet everything...a missed flop OOP with several villains is a tough place to c-bet. Checked to you on the button is a great place to c-bet. I play every table a little differently depending on the mixture of players...if everyone is tight/weak then a c-bet always folds them out if they miss. As such, I will c-bet just about everything. However, if there are a few LAGS and calling stations, you need to be careful about what you c-bet.