Yeah, the secret of bluffing, I love it!Watch the board, what has your opponent? did he bet on his King? does an Ace show up?
Does he have Aces and is afraid to be destroyed again by the straight or flush that developped on the board? In that case go all in IMMEDIATELY and rapidly as soon as the card turns up. But be aware of your readings and your opponent, he might have set up a trap on you three rounds ago
The essencial: don't bluff an experienced player, when the turn/river did not set up a complete change of situation
Make it the one and only card you've been waiting for! Don't threaten him with your last 2000 chips, if 24000 are already in the pot and he has 40.000 more. Choose your spots, bluffing is essencial in poker, ask ryder