You need a specific reason to trap.
IE, limping under the gun with A/A early in a tournament is begging for trouble. But if you're up against a short stack and you're looking to knock him out, then slow playing is OK. Shorties are desperate and will shove with stuff like middle pairs, so you want to give them the opportunity to hit something like that.
Basically, against one player you slow play someone who will make big moves with substantially worse cards.
Against multiple players, you only slow play extremely powerful hands when they are very unlikely to outdraw you (no straight or flush draws on the board that can beat you). In the latter case, basically you're hoping that someone will turn or river TPTK or two pair so can stack them.
But you have to realize, that getting outdrawn isn't the only way to get burned. Lets say you flop the nut flush, or the nut straight. Betting out might get called by hands you have beat. But turn/river might put a 4-to-a-straight or a 4-flush on the board, scaring off hands that might have called bets on earlier streets.
It seems obvious, but the best move is what gets them to put in the most chips while they have the worst hand.