If you're playing ring games then FyrFyr998's advice is sound but in SNG's you have to loosen up at times, early on when the blinds are tiny you can play some rubbish in unraised pots as the implied odds of hitting something good make it worthwhile and late on when there are only 3 or so left you have to loosen up again as they won't have great cards that often. And of course position is still very important.