What I do and recommend you do, is to gamble on whether or not my opponent is bluffing. What I hold isn't all that important; it only has to be able to beat a bluff. As I gain experience, I'm constantly being surprised by how often players bluff. Missed Flush draws are somewhat predictable of course (if only two of a suit is on the board, nobody has a Flush) and missed Straight draws are fairly evident as well. More difficult to determine is the bluff where your opponent holds second pair, but is representing top pair and you hold top pair with a poor kicker. As an example, let's say you have

-5h and the flop is

,Js,7d. Your opponent bets into it and you raise. If he calls your raise, you have got to at least suspect he also has a King and, if he does, his kicker may be better than yours. But don't forget that he might be holding Q-J here and is hoping for either a J or Q to come on the turn, which is evidenced by the fact he didn't re-raise. Let's say the turn card is 10h. If he now bets into you, it could mean he has either made a Straight (from a hand of A-Q or Q-9), hit two-pair (from a hand like K-10 or J-10) or has a Straight draw (from a hand of J-Q). I would just call here, unless I had a lot of chips, in which case I'd raise in light of my Flush draw. Either move is a gamble, but I think it's a reasonable gamble. I still have top pair and, unless the river card makes my hand totally untenable, I'm going to call his river bet, assuming he makes one. Of course, if the river makes my Flush, he's getting it with both barrels, should he bet. Yes, he might have A-x of hearts, but that's a chance I'm willing to take. After all, I'm gambling, right?