You have to provide a bit more information there. Live or online? Do you pay attention to your opponents' betting patterns? Typically if you flop a monster, it's best to slow play it, and give your opponent enough rope to hang him/herself. On the flipside, if you flop a set on a board with two or more suited cards and/or overcards, a 2/3 or larger pot sized bet should be set to prevent the quintessential suckout or giving your opponent the right odds
to improve their hands. Slow play on a non threatening board, and play aggressively/cautiously with additional players or a board that could allow your opponent to lay a bad beat on you.