You can get clues to what other people have from the betting. Sometimes enough and you can fold, sometimes not enough and you lose. If somebody bets or calls, you have to ask yourself, "What hand that called the pre-flop betting would do that?" A set is usually in the mix. If you have a set and somebody has a bigger set, the tell is usually when they take all your money at showdown.
I just knew this was going to be, "I can't find the passwurd enywere!"