Blind stealing is an important part of no-limit hold'em tournament play. If you don't steal blinds occasionally, especially when the values of the blinds in relation to the sizes of stacks has increased, you can quickly find yourself short stacked. Also by not stealing blinds, which is actually a form of a bluff, the other players will be able to gain a more accurate picture of your style of play.
Stealing is best attempted from late position. Dealer or cutoff (to the right of the dealer) is a fine spot to steal from. With late position if one, or both, of the blinds call you will continue to have position after the flop. Following through on your steal attempt after the flop might win you the pot. Only your read of the callers play and betting patterns can tell you whether to follow through after a failed blind steal.
Stealing from the small blind is riskier. If called, you will be out of position and first to act for all subsequent betting rounds. Also some players dislike giving up thier blinds without a fight, especially to the small blind player.
A good question is how much of a bet is required to steal the blinds. This does depend upon the players at the table. A general rule of thumb is a bet of 2.5 to 3 times the big blind is enough. Thus a $300 bet when the big blind is $100 is about right.
Stealing early in a tournament, when everyone's stacks are deep (100 times the size of the blinds), involves exposing yourself to risks for minor gains. The best advice is to wait until the blinds start meaning something, when stack sizes are under 20 or 25 times the big blind.