You won't get anywhere in Texas Holdem if you can't read the flop properly.
Reading the flop means knowing what hands it makes possible, knowing what your own possibilities are as well as your opponents'. You must also understand how the texture of the flop influences the game; that is, how threatening the flop is - to you as well to your opponents.
There are a number of patterns you need to look for on each and every flop. They may show up alone or in combinations. Each of those patterns, or structures, gives rise to a certain type of post flop play, all of which you must learn to master.
Let's walk through those patterns one at a time.
If there are three cards with two gaps or less between them, someone may have a ready-made straight. For example, if the flop comes 9-8-5, T-9-8, or 3-2-A.
Of course, the chance that someone actually has a made straight depends on what precise cards arte required. Q-J-T makes a lot more straights than 7-5-3, since it's much more likely that someone who has stayed in to see a flop has A-K, K-9 or 9-8 than 6-4 in the hand. Hands like 6-4 are very often thrown away preflop.
This kind of board is pretty infrequent though, and if it's you who have the straight, you typically won't get a lot of action from the opponents, since the straight is so obvious and the pot is usually relatively small at this stage.
If all three cards are of the same suit, someone might have a made flush. Just like with the straights above, this doesn't happen often, and if you have a flush here you often won't get paid a lot, unless an opponent has another flush that is lower than yours. Which is really rare.
When you flop a made straight of flush, you may be tempted to slow play it in order to entice a bet from another player rather than scaring everyone off. That might be okay, but don't overdo it. Your hand is never the absolute nuts, there are always cards that may come on the board that will look really bad for your hand.
For example, if the board pairs, your flush may not be good anymore, or if you have a straight and the board flushes.
Pairs on board
With a pair on the board, a lot of dangerous hands become possible: quads and full houses as well as trips and two pair. Once the board is paired, the value of straights and flushes go down, the value of straight draws and flush draws too.
If you get a lot of action on a paired board, you must be able to lay down for example a flush. At the same time, a paired board is a good bluff opportunity, both for you and your opponent. So don't fold your flush automatically. Think it through!
Also remember that when a pair is on the board, hands like three of a kind and two pair are much weaker than if the board is un-paired. You may be up against one of those super strong hands just mentioned, or else someone may simply have the same trips with a better kicker.
If two board cards are within two gaps or closer, someone may have flopped a straight draw. This means that if you have a made hand, like two pair or trips, you'll need to protect your hand. Meaning, you have to bet properly to put any drawing hands to the test.
This doesn't mean that you should bet twice the pot or even move all in, that may be a bit over-protective. Just make a well sized bet so you don't give away free cards to the drawing hands. Then, if a card arrives that could have filled someone's straight, then you need to decide if it's actually the case or not. It's not easy to separate made hands from bluffs - but that's poker.
Flush draws are possible as soon as there are two cards of the same suit at the board. Just as with straight draws, a made hand needs protection through a decent bet.
If you flopped a flush draw yourself, you should be aware that there are usually nine cards in the deck that will make it for you, which means you have odds 4-1 on the next street and 2-1 if you get to see two more cards.
Also realize that if you make a flush on a later street, you'll often not get paid very much since the flush is pretty obvious. People notice when there are three hearts on the board, and they typically won't give you much action. Unless they happen to have a strong hand, like a lower flush.
Straights are often much harder to see. Imagine a flop of A-8-4. You bet out with A-K and get one caller. The turn comes a 6. The pot is getting bigger, and you want it. You bet and the opponent re-raises. Would you really put him on 7-5? It's pretty hard to believe. Also, players often may not even notice that a straight has become possible.
If a player draws to a straight and a flush simultaneously, there may be as much as 15 cards that fill at least one of those hands.
Of course, both potential straights and potential flushes give players opportunities to bluff. If you consider drawing to a flush, check if a straight draw is also possible, in which case you have a second way out if you don't make your flush: representing the straight.
High cards or low cards
If the pot comes with one, two or three high cards, chances are that someone has made a connection to his or her hand. At the flop, high cards are much more likely than low cards in players' hands, since people tend to fold hands with low cards preflop.
This kind of flop leads to a lot of action, and you have to be well aware of your chances as well as the dangers involved. Fasten your seat belt!
High cards also present you with some bluff potential, since they look scary to the other guy. Of course, this is a sword that cuts both ways.
On the other hand, if the flop holds low cards only, it's very possible that it missed all players. If you raised preflop with a high pair, you're probably still good after a low flop, even if it actually missed you as well. You can play your overpair strongly here.
On the other hand, the fact that it's hard to lay down premium starting hands against low boards has given rise to a whole new strategy concept - set mining. This consists of taking flops with low pairs and hoping to hit a set. Then the idea is that your opponent who's playing a strong starting hand will pay you off big time even though he missed the flop, since he can't get away from his premium hand and the low board looks innocuous.
For set mining to show long time profitability, a few requirements must be in place. The opponent must have a strong hand. For example, a raise in early position from a tight opponent is a good signal of strength. Also, both you and the opponent must have big stacks, so you can win really big when you hit your set - to compensate for all the times when you miss (7 out of 8 times).
Combining the board and your hand
As a last step in the Texas holdem flop analysis, you should compare the board to your own hand. This can led you to some pretty strong conclusions.
For example, if the flop comes Q-J-6 and you have a pair of tens, the risk for straight draws is much decreased, since you hold half the tens need to form a straight. You have straight blockers.
Or if a player raises preflop, you have an ace in your hand and the flop comes A-A-5, it's suddenly quite unlikely that the opponent has an ace - there's only one ace left unseen.
Once you have learned to read the board, this kind of combined analysis is the next step to perfection in Texas Holdem.