Observe your opponents and base your conclusions on those observations.
If you see that a certain player always raises on the button when it is folded to him, but in other positions plays quite tight, you can be sure that the majority of the time he is trying to steal. Of course sometimes he will have a hand, but this will be much less the case.
For yourself to know when you should steal depends again on the players to act behind you (in the BB, SB and maybe even the button while you are the CO). If you see that they are tight or weak, you should definitely try to steal. If they are calling stations, nevermind the stealing.
Also, in the beginning of a tournament, usually you shouldn't try stealing as you don't know your opponents and the blinds are very small compared with the stack sizes (much less chips to be won there). Later on, when ante is in play, it becomes much more interesting to steal (instead of 1.5 BB, you will be stealing 2.4 BB in a 9 handed game).
Of course, if you have a good hand and you're in late position, you should play it the same as if you were stealing, only this time, people might think you're stealing and more chips can be gained.
Betsizes when you're stealing and when you're raising for value, shouldn't defer, so you don't give any tells
about your hand. Don't shove to steal the blinds if you have a big stack and no good hand. This is a losing proposition. Just play it the same way as you would play a good hand and you're trying to get some value.
If you're a small stack, stealing becomes more dangerous, as people will call you lighter because the cover you. However, your range should get wider in late position (same for being a big stack actually), and shove/fold play is recommended, but not to steal in the idea of having no hand and trying to fool them.