If you have stayed in the hand this long, it had better be because you think you have the best hand, you know you have the best hand, or you were on a draw for what would definitely be the best hand (i.e. a Nut Straight or Nut Flush draw). You may still be in the hand because there has been no betting on the flop, but those situations are relatively rare.
Remember that the most costly hands in poker are not those hopeless cards that you pick up 75 per cent of the time; they are the quite good hands you see 20 per cent of the time and you over-value, staying in the pot too long, committing too much money to the pot and then finding it hard to throw your cards away and wave your money goodbye. The most dangerous hands are the second-best hands – because you think that they might be best and then they win you nothing and lose you the most. Therefore, unless you are confident that your hand is best, or will be best on a reasonable draw, if there is a bet from an opponent just throw your hand away now.
On the turn, if you have a hand that you think is best, do not let your opponents get to see the river for free – if they hit their card on the river, you may have converted a winning hand into a losing hand and then find it very hard to judge at the end.
For example:
you hold A(S),Q(C)
and the flop comes A(C),6(D),2(C)
As you have top Pair with a good kicker, you put in a bet on the flop and you are called by one opponent.
The turn comes 8(D) A(C),6(D),2(C)
If you believe you still have the best hand, you should put in another bet and make your opponent pay to see the river card. If you check and he checks, the river appears for free and he may make a Flush or 2 Pair without having had to pay for the risk. For example:
He might hold A(D), J(S)
or K(C),10(C)
and the river comes J(C) 8(D),A(C),6(D),2(C)
With either of the above hands, you have now been beaten by your opponent: with the first hand, he has 2 Pair – aces and jacks; with the second hand, he has the Nut Flush.
If you had raised the value of the pot, your opponent should certainly have thrown away the Flush draw hand (since he has only a 1/6 chance of making his Flush with one card to come) and he might even have conceded with his AJ.
Either way, to let your opponent see free cards when you think you have the best hand is a mistake.