If you are playing from the small blind at the no-limit holdem tables, remember whatever your actions before the flop whether you fold, flat call or raise, you will be out of position at the table for the rest of the hand and therefore at a disadvantage, so you want to minimize any losses you may incure.
The worst problem that players make is falling into the trap of completeing the small blind too often with weak or marginal hands. It is tempting as you have already contributed half the blind to the pot, so why not pay a bit more to see the flop?. As stated before, being out of position for every other round of betting is going to put you at a disadvantage.
Your first consideration should be how good is your hand. To be able to play correctly from the small blind you need to be holding an above average hand, A-A, K-K, Q-Q, and A-K. These hands will give you the option of being able to call a raise or even raise yourself. If there is a raise before you, it would be wiser to fold most hands.
If you are in the situation where every player folds round to you, this will give you the opportunity to raise the big blind and steal the pot, but this in itself will present problems. When you raise from the small blind to steal the pot, ideally the big blind will need an above average hand to call your raise, but if the big blinds suspects you are trying to steal the blinds, they may well try and reraise you putting you at a disadvantage. If you just complete the big blind this will give the big blind the chance to raise himself and steal the blinds. The best strategy to use when everyone folds to you is to mix up your play, raising and flat calling with a mixture of hands, premium hands and average hands but always be prepared to fold to a reraise if you think your hand can be beaten. Mix these plays up with folding your weak hands and you will soon be able to get a read on how your opponent plays in the big blind position.
If a few players limp round to you and you have a decent enough hand, you are getting good odds to see the flop, so it is worth completeing the blind. If you are holding a monster pair, now is the time to fire in a big raise and try and take down the pot there and then.