Players get excited when they flop two pair because they know they're in a great position to take down a pot. But often, two pair is not nearly as powerful as it seems. This is especially true when holding bottom two pair or top and bottom pair. These hands may look dominant on the flop, but they're usually quite vulnerable.
For example, say you're playing a No-Limit Hold 'em ring game. There's a standard raise to four times the big blind from middle position. You figure the player has A-K or maybe a middle or high pocket pair. Everyone folds to you on the button, where you find 5d-7d. You've got favorable position and a hand that can flop some powerful draws, so you decide to call. The blinds fold, and the flop comes 5c-7h-Ks.
This is great. Not only do you have two pair, but it's very likely that your opponent has a piece of this flop, with top pair top kicker or maybe an over-pair. He bets into you, and you have to decide what action is best.
I've seen some players smooth call in situations like this, but that is not a wise play. When you have bottom two pair and your opponent has an over-pair or top pair/top kicker, you're not as big a favorite as you might think. Your opponent has five outs - cards that will counterfeit your two-pair - which gives him a very live draw. You're a 75% favorite to take the pot, and that's great, but it's not the type of statistical edge that justifies slow playing.
The better play is to raise and put your opponent to a decision right there. Many players overplay top pair and over-pairs, and will either call or re-raise all-in. That gives you the chance to put all of your money in the pot as a big favorite. If he puts a bad beat on you at that point, so be it.
Is it possible your raise will force your opponent out of the pot and kill your action? Sure, if he's sitting with a pair of Queens or Jacks he'll likely fold, but against that sort of hand, you'd have no chance to win much of a pot anyway. Your opponent would probably check to you and then fold to any bet on the turn. And as Howard Lederer pointed out in a recent tip on playing sets, if a blank comes on the turn and you raise at that point, you'll be sending an indication that the turn card helped you in some way. He'll have to assume that his lone pair is no good.
There will be occasions when you flop bottom two pair or top and bottom pair at the same time your opponent catches top two pair or a set. When that happens, you're going to go broke. In fact, you should lose your stack in most situations like this. If you're not willing to risk a lot of chips in this kind of hand, you're probably not doing enough to maximize your pots when your hold the best hand.
When you find yourself holding two pair, play them aggressively and get your money in on the flop. It's the surest way to get the maximum profit from a strong but vulnerable hand.