"UNLESS" #1
The first "unless" rule of bluffing is "unless you have a solid read on your opponents." If you're playing a tight table, you're in a solid position, and you're sure your bluff can take down the pot, then a quick steal may be in order.
"UNLESS" #2
In poker as in real estate: location, location, location. Playing a bluff should be as much if not more about your position"UNLESS" #3
Simply put, there are various forms of bluffing that may not be considered as bluffing in the purest sense. To me, bluffing in the purest sense is when you have absolutely no chance to win. I mean, the river card has been laid, you can't even beat what's on the board, and yet you represent that you not only do you have a hand but you have THE hand that the other players would fear that you have.
So if that's the extreme of bluffing, is everything else on the bluffing chart really bluffing? Let's look at a couple variations on the bluffing theme.
LIMITED BLUFFING
Limited bluffing is that bluff that comes late in a hand against as few opponents as possible. And it starts with a good hand. There was actually a time, in the early betting rounds, that your bet wasn't a bluff at all. Maybe you were on a draw, hoping to pull that last diamond for a flush. When the river comes and you didn't get it, you decide that you don't want to go down meekly. You think there's a chance that betting will scare off your opponent. This isn't a pure bluff. It really only became a bluff on the river. And it's very calculated. But because you have no chance of winning, it is a bluff.
SEMI-BLUFFING