Yep, rilla is right. Always raise to gain information. Before the flop comes you should have some estimate (based on your reads) of what cards your opponent is holding. Continuation bets are about half the pot. By looking at a flop you should be able to decipher whether it was a good flop or bad flop in relation to your opponents possible holding. If you think it helped your opponent and your left with an Ace high fold it...

On the other hand, theres a probe bet. When your last to act and your opponent checks it. Throw in a probe bet usualy 1/3-1/2 of the pot to see where your opponent stands. Constantly test your opponents and there hands, these bets easily pay off in the long run.