Check-raise
Check first, then raise after your opponent bets. A trap with teeth.
You're in the big blind with 6♣6♦. The cutoff raises, you call. Flop: K♠6♥2♦. You've flopped a set, and it's invisible - the flop looks like top-pair country, and nobody puts the big blind on three sixes. You check. The cutoff reads weakness and fires a continuation bet. Now you raise big. On a board this dry there are no draws to chase, so it's simple: any king calls and pays you off, and a bluff that fired at a checked pot has to fold and leave its bet behind. That's the play - let the aggressor build the pot, then take it over.
Leading out tells the table you like your hand, so anything with nothing folds before it puts in a chip. Checking tells them nothing, so they bet hands that would never call a raise cold - and those are the hands you raise for value. It also punishes the auto-c-bettor: a player who fires at every checked pot regardless of what he hit is exactly who a check-raise eats alive. As a bluff it runs the same way in reverse - check a scary card, let a cautious opponent bet a marginal hand, and the raise takes the pot on the spot. But that version needs real fold equity, since a call leaves you drawing.
The common mistake is doing it only with monsters. Check-raise with the nuts and nothing else, and any awake opponent stops betting into your checks - now the trap catches nothing. The other mistake is sizing it too small. A raise that barely doubles the bet doesn't grow the pot or price anyone off. It just flips your hand face up for a small profit.