When to slowplay...
1. When you have the stone cold nuts. Your hand on the flop is either unbeatable or very unlikely to be beaten. If you flop four aces you can bet right out, but serously your opponent has to have something to call right? Not likely with a flop like that.
2. You know your opponent to be aggressive and checking will surely induce a bet.
3. You suspect that a player may be slowplaying you. This is the quagmire. If you bet they call and you get no info. You check and they check. These hands always lead to a disaster on the river. The reason I suggest slowplaying, is because you can save some money if you make a correct read and they DO have a monster. Sometimes this is the only way of avoiding a "cooler " hand.