If we want to win at poker, we have to win enough pots, or at least enough large pots. We just can't win a profitable amount of pots only having the best hand because the deals are not going to give us the best hand often enough. This means that we have to win a pot now and then without the best hand. We have to bluff at least once in a while.
The point is also made above that if we never bluff we will have trouble getting paid when we are strong. After 2 or 3 or 4 times an opponent calls us and loses to our strong value, he realizes that we only bet when we have it, so we end up telling him that we have it when we bet and he has an easy fold. We have to mix some bluffs in to keep him guessing. This is the essence of showing balance. Villain hates us when we are balanced because he's always in a tough spot when we bet, not knowing if we are strong or if we are full of it. We are difficult to play against and this is good.
So when to bluff? In order to bluff, there has to be a hand ahead of us that might fold, preferably a few hands. If we have A-high and the board is QT742, 2x 4x, 7x, and Tx as well as hands like 33 and 55 all might fold here. This is a possible bluff spot. On the other hand, if we have top set but there are 4 spades on the board, no hand better than us is folding except maybe a really weak spade, so this is not a good bluff spot.
Villain's who check the flop out of position can often be bluffed, especially if we are the PFR. This is the most common bluff in hold'em.
Bluffs work best heads-up. It is twice as hard to get 2 Villains to fold as 1. Just imagine how hard it is to fold out more.
A bluff usually has to rep something on the board or just strength in general. This is why scare cards are our friends. For example, if the flop is checked and an A hits the turn, we can bet and Villain will often fold because he thinks you have an A. Paired boards make great scares, even better than completed draws and less risky too.
Bluffs work best when they are backed by previous street aggression because this aggression reps itself. When we barrel our bluffs we are repping overpairs, sets, etc that may not be clear on the board.
Like in any pot, if we can plan for multiple ways to win, we need to do it, and this is never more important than with bluffs. The concept is semi bluff or
equity bluff. Let's say that we have flopped a flush draw. We can bet this even though we have nothing. If Villain folds, great but if he calls, at least we might still hit our flush, and if we do the pot is now bigger. ; ). On the other hand, if we bluff with complete air and get called, we lose 100% of the time.
Sizing for bluffs is tricky. How much should we bet? Well there is a zen thing here. Like Charlie Carrell says, our bluff size is the smallest amount that will make Villain fold. This is usually a larger size. Small bets are just too easy to call. If it is cheap enough, Villain might call us just to see our cards and put a bluff frequency on us. The amount to bet will depend on Villain tendencies, pot
odds, stacks, proximity to the bubble etc. Most of all, Villain's actions on previous streets will tell us. If Villain has been passive in the hand, he will be more likely to fold and a normal bluff size will usually be best. If Villain has been barreling aggressively, it will probably take a lot more to bluff him off of his hand, and we will need a good scare card too. In fact, if he is that strong we may not want to bluff him at all. But our bluff sizing is the smallest amount that we have reason to believe that will make Villain fold. Anything larger than this is just extra risk if we get called. And we will get called and lose now and then (hopefully not too often). That is just part of the game that we must accept.