Counting your outs
An out is a card that will improve your hand to a winning hand on the river based on the traditional poker hand rankings. A hand with a lot of outs before the river is often a very good hand even though it hasn't yet achieved anything in terms of the traditional hand rankings.
For example, a no-pair hand on the flop that has a flush draw, a straight draw, and two overcards is a much better hand than top pair on the flop even though one pair beats no pair. That's because that hand with all the draws is the probable winner at a showdown on the river, after two more cards have come. It's a hand with a lot of outs.
The breakeven point between a pair and a draw is 14 outs on the flop. A hand that has 14 outs on the flop is a slight favorite over a hand with one pair and no redraws on the flop.
That would mean hands like:
bottom pair and a flush draw (14 outs)
a flush draw with two overcards (15 outs)
a flush draw with a straight draw (15 outs)
a straight draw and two overcards on a rainbow flop (14 outs)
are pretty good hands to have on the flop.
Note that when I counted a straight draw I specified a rainbow flop. That's because a hand like 8c7c on a flop of 2d 5d 6s doesn't have 8 clean outs to make a straight. Two of the cards that will make it a straight will put three diamonds on the board, possibly killing the straight by giving someone else a flush. You can't really count those 8 outs as an improvement to a winning hand. I count the straight draw on a two suited flop as 6 outs, 7 outs if you have a backdoor flush draw (such as a 6c instead of 6s in the above example).
Counting outs for straight draws can sometimes be problematic. Not only might your straight draw give someone a flush, it might give someone a higher straight. So it's best to be very conservative when counting outs on a straight draw. That's the case in both limit and nolimit forms of hold'em, but it's especially true in nolimit becazuse of the potential cost of making your hand and losing anyway.
Dawn, of I had Outs, recently described a hand she plays which serves as an example of what I'm talking about.
On the button I get 9c8c, I raise to fifteen. Now, I haven’t raised in hours, no one has seen me do anything but listen to my ipod and drink Grey Goose with pineapple. And yet, six people call me.
The flop is a lovely TcJcAs I bet out $40, I get two callers. Qh comes on the turn. I bet $50 and the guy in the one seat raises all-in. I have like $92 left.
Although she's right that a flush draw with a straight draw is a god flop for her, it's not as good a flop as she thinks it is. She effectively has something like 11 outs, not enough to make her a favorite against even bottom pair. A queen will make her a straight, but it's a very dangerous straight. Anybody with a single King will make a bigger straight with that card (which, of course, is the card the guy in seat one has).
She should have at least thought about checking that flop, keeping the pot small so that should a queen fall it probably won't cost her all her chips to draw for that flush. I'm not saying she should have checked, I'm saying should have given it some serious thought.