After the flop, your hand is pretty much defined. Before the flop, you have seen only 2 cards out of the total 7 cards that will eventually be in play. The flop gives you 3 more cards, so now you are seeing 5 out of the 7 total cards that will eventually make your hand. As a result, the strength of your hand will change far more on the flop than it will on the turn or river, with the exception of those times that you draw at a flush or straight.
For instance, before the flop an Ace and King of the same suit, such as AhKh, is a good hand, with potential to become a huge hand. After all, with a great amount of luck it could turn into a royal flush, the best hand possible. A little more likely is something like top pair, with the best available second card, a pair of Aces, with the King as your second card (kicker), still a very good hand. However, if the 3 cards on the flop are 2, 6 and 9, with no hearts, you have nothing but a weak draw. The best you can hope for is that it is checked around, and an Ace or King comes on the turn. Your great potential has turned to trash, and if there is a bet you should fold unless the pot is very large.
At the other end of the scale, you could start with something like a J and Q unsuited, which you would hopefully only be playing in 1 of the last 2 positions or the blinds, which is a weak starting hand. However, if you get lucky and flop something like J, Q, Q, your hand has just gone from marginal to monster. In a case like this, your decision changes from one of �should I stay in� to �how do I get the most money in the pot�.
The result that will occur most frequently is that you put in a raise before the flop with premium cards that have an opportunity to turn into a big hand, or you call a bet in late position with a weak, speculative hand like a suited connector, and once you see the flop, you have nothing. In this case, you must check and fold.
This is the reason for only playing speculative hands in late position for one bet. They will not usually turn into anything and you throw them away, so you don�t want to put in a lot of money which you are probably going to lose. The large premium hands will however end up turning into a good hand much more often, so you raise with those to get more money in the pot because you expect to win it.
After you see the flop, one of several things is going to happen.
1) After the flop, you have nothing. You have no pair, no draw to a straight or flush, and there are cards on the board that are higher than yours. For instance, in late position, after 3 other players have called, you call with a Jack and Queen of 2 different suits. The flop contains an Ace, a 9 and a 3, all different suits. Note that if someone has an Ace, your only hope is that both a Ten and a King come to give you a straight, or both a Jack and a Queen come, to give you 2 pair, or perhaps 2 Jacks or 2 Queens to give you 3 of a kind. In the latter 2 cases, your opponent could be holding an Ace and either a Jack or Queen, so you would still lose. The decision in this case is very simple. Check and fold to a bet.
2) Once you see the flop, you have a huge hand. For instance, you started with a pocket pair, and hit a third of the same rank, giving you a set, or you flopped a flush or straight, or you hit top 2 pair. Once again, the decision is easy, bet and/or raise. There may be an occasional case where you want to slow play, i.e. check and just call a bet. For instance, you raised before the flop, hit a third ace, and it seems unlikely that anybody could have a hand where they could call a bet. However, at the low limits, there is no need to be tricky. The players will call bets and raises even when it should be obvious that they can�t win. One of the worst things that can happen is that you hit your huge hand, while someone else hits a very good second best hand and would have raised, so you cost yourself money. Of course the worst thing that could happen is that you let someone draw cheaply, or for free, and they end up beating your huge hand. This is very expensive, because your slow play cost you the entire pot.
3) You have a good, but not great hand. For instance, you raised before the flop with a pair of jacks, no cards higher than a Jack came on the flop, and there is no flush or straight likely. You probably have the best hand, but it is vulnerable to bad cards appearing on the turn or river. Any Queen, King or Ace that hits the board may give someone a higher pair, and the board could develop into straight or flush possibilities. Ideally, you would like the person on your right to bet, so that you can raise, giving everyone else the situation of having to call 2 bets instead of 1. You may have to try for a check/raise in order to face people with calling 2 bets. You can only try this if you think someone will bet after you check. If you are not sure that someone after you will bet when you check, you should bet. What you want to do if possible is to get players with an Ace, King, or Queen to fold. At the low limits, this is very unlikely when they only have to call 1 bet. Some of them will call all the way to the end with an Ace and any other card hoping that you are bluffing. You may however get someone to fold small cards that would have turned into a straight, a flush, or 2 pair if you had let them draw for free, and this is still a good thing.
4) You have a mediocre hand, such as top pair with a poor second card, or you have the second or third pair. An example of this would be when you call from late position with A7 suited, hoping for a flush draw, and pair the ace, with none of your suit showing, or call with a small pair like 44 or 55. Most of the time, these will be losing hands. Especially if there are several players in the pot, there is likely to be someone with an Ace and a better second card, putting you at a huge disadvantage. In the case of the small pair, you are hoping to flop a set (hit the third card, such as a third 4, or third 5) If there are several people in the pot, and there is a bet before you play, just fold. If it is checked around, and no card comes on the turn that would seem to help anybody, you may want to try a bet and see if they all fold. This is most likely to work if there are only a few people in the pot. The more players there are in, the less likely that they will all fold. You must also be aware of how the players play. If you have a player that will call to the end with a slightly better hand, it may not be worth a bet. Also, if you do bet on the turn, and get raised, fold. Not very many players at the low limits will check raise as a bluff.
5) A situation that happens often is that, after the flop, you either have no made hand, or a very weak made hand, but you have possibilities for improvement. For instance, you call from late position after 4 others have called, with an Ace and 6 of hearts. The flop contains 2 hearts, but no Ace or 6. You are drawing at the nut (best) flush. If you get another heart, you will probably win the pot, otherwise you will most likely lose. To make a decision with drawing hands, you need to consider pot odds, implied odds, and your odds of making the hand you are drawing to, and winning. Note that in many cases it is quite possible that you will make the hand you are looking for, and still lose. And extreme example of this would be hoping to hit a 9 to pair the one you are holding. This would of course lose to anything, pair of Tens or better, and is a bad idea. A more practical example is drawing to an open ended straight, such as 8, 9, T, J, with 2 cards of one suit on board. If either a 7 or Queen hits, you have a straight. However if that 7 or Queen puts 3 of one suit on board you may lose to a flush. As well, if the 2 cards that you have are the 8 and 9, someone else may be drawing to a better hand, with a King and Ace for instance, in which case the Queen that gives you a straight gives them a higher straight at the same time, and is going to cost you some money. As we will see when we talk about counting outs in another article, you must take these possibilities into account when calculating your odds.
There are many more factors that need to be taken into account in each situation. How the other players play, position, the size of the pot, the exact makeup of the flop etc. These will be covered in more detail in future articles. For the moment, this should get you headed in the right direction.