Have you ever wondered how it is that good players seem to snap off opponents’ bluffs with monotonous regularity, but fold when the opponent “has the goods”?
The answer is not that complicated. The bluffs they beat are the bluffs typically tried by inexperienced and poor players. Invariably these occur when a hand has “gone wrong”. The bluff normally consists of a bet on the river “because there is no other way that I can win the hand”. You need to know these skills to play online poker for money.
The principles of bluffing:

1. Make sure that your play of the hand has been consistent with a hand that beats your opponent
2. Do not bluff just on the river, except in no limit for a large amount relative to the size of the pot (and then only when you are last to bet). Bluffs are best set up in advance, like a good lie. They need surrounding veracity to make your opponent believe.

An example from Limit $5-$10 game.
Hero (you): As Kh
You are in a middle position.
The player on your immediate right calls. You raise. The small blind, whom you have observed to be an inexperienced player, calls. The big blind folds. The early-position limper on your right calls. $35 on the pot ($10 from each of the active players, plus $5 from the folded Big Blind).
Flop:
Qs Td 5s
Small blind checks, Limper checks, and you bet. Small blind now springs to life and raises. Limper folds and you call. $55 in the pot
Turn:
Qs Td 5s 6h
To your surprise, the small blind now checks. You check as well. You had been expecting a bet here. The only logical explanation for this check is that your opponent has something like King-Jack or two spades, or maybe even King-Jack of spades.
Therefore he raised on the flop in the hope that this would allow him to see the turn and river relatively cheaply. However, you decide to check as well. The main reason to do this, even though you suspect that you are ahead, is that if your read is wrong you may be check-raised again.
River:
Qs Td 5s 6h 6d
Your opponent now bets. You call in the blink of an eye and he says “I missed”, showing his King Jack. You show your Ace-King high and everybody thinks that you are a genius.
But your play was quite logical. What other kind of hand could your opponent have? His bet on the river was a classic “this is the only way I can win this pot” bet. You see it time and time again, and it is a classic example of how not to bluff. Note also that you do not have to be right every time. You don’t even have to be right half of the time. You are putting in $10 and winning $65 as a result. Provided your read is correct one time in six or better, you will show a profit from calling here.
Is the answer therefore, “never bluff”? Definitely not. In fact, the bet by the player with the Ace-King on the flop is a form of bluff. A “continuation bet” in no limit poker (where you raise pre-flop and bet out about half the pot on any flop) is a kind of bluff. People bluff all the time, because they miss their flops more often than they hit, but they bet anyway.
But these are not “last throw of the dice” bluffs. They are more a “well, I missed, I’m probably behind, but I might end up in front, and, if I bet, my opponent might fold” kind of bluff.
Are there any times that you should try a “last throw of the dice” bluff? Definitely. Another old saying in poker is “never bluff a duffer”. As with most old sayings, it is sometimes false. Bluffs have to be set up in advance, so that your hand could, quite logically, be something which slaughters the best that your opponent can have to offer.
Suppose you are on the button in a no-limit game and have any two cards. Say, 87 of spades. Since you do not plan to be called here, your holding is irrelevant. You call a 4xBB raise by a player in middle position. You have noted that he is a solid player who is willing to call big bets, but is also willing to lay down a good hand. Both of you are quite deep-stacked. Your opponent also knows that you are capable of calling raises, when you have position, with any number of hands.
Flop:
9d 4s 3d
Your opponent bets three-quarters of the size of the pot and you immediately call.
Turn:
9d 4s 3d Jd
Your opponent checks and you bet the size of the pot, making sure that you have enough to bet the pot again on the river if your opponent calls. But he doesn’t call; as you hoped and expected, he folds. From his point of view, there is no reason why you should not have two diamonds. Your play has been quite consistent with having a drawing hand. And there is a good chance that your opponent has missed the board has well.
Let’s move back a card and look at your thought processes when you call your opponent’s continuation bet on the flop.
If you hit a seven, a two, or a diamond, then you have a card which scares the hell out of your opponent. A five, a six, a nine, a three or a four will also have him worried. Since you do not have a diamond, that gives you eleven “outs” rather than the nine you would have if you were really drawing to a flush. Add to that two threes, two fours, three fives, three sixes, two sevens, three nines and you have 26 cards that scare the hell out of your opponent out of the 47 unknown cards in the deck. You are odds-on to hit a card which, if you bet the pot, will probably make your opponent lay down a pair of aces. And all because you put in a bit of forethought.