If a player checks, that can mean three different things:

• His holdings are weak, and/or the flop has not helped him and he intends to fold when someone bets
• He has a mediocre hand (like low or middle pair or a weak draw) and he intends to call a bet from somebody else but doesn’t want to risk a raise from someone else
• The player has a good or very good hand (Top pair or better or a strong draw) and he intends to raise a bet from another player to fill the pot. A check-raise is a strong move and means a strong holding most of the time. On the lower levels its almost never a bluff, and it should be respected accordingly.

A bet from a player normally means that he likes his hand and that he sees good chances that his hand is winning. If someone bets into only one or two players, he might also be trying to bluff to make you fold.
If a player raises another player’s bet, you can assume that he is having a good hand. You need an equally good hand to call unless you have informations that convince you he is bluffing.

In order to choose your own actions, ask yourself the following questions:

• Is my hand likely to be the best hand?
• If it is, how likely is it that my hand will be beaten on the turn or river?
• If you have a draw – how many outs do I have, will my draw be the best hand if the next card hits my draw, and how are the pot odds?
• Do I want to have multiple opponents or is my hand stronger heads-up?
• If I call or bet, is somebody going to raise behind me, and if someone does, do I welcome this raise and would I call or even re-raise?

Post-flop, you should check:

• When your hand is weak and you want to try to see the turn cheap (check/call) or for free (if it is checked through)
• When you fear a raise behind you and your hand is good enough to invest 1 bet but not good enough to invest 2 bets
• When you think you are holding the best hand and it is safe to assume that somebody behind you will bet so that you can raise and thus put more money in the pot. Watch out – if it is checked through, you have given your opponents a free card and you have lost money.

You should bet:

• When you think your hand is likely to be the best hand
• When you see a good chance that all your opponents will fold (even when your hand is weak, but try this only against one or two opponents)
• When you have a draw that has good or very good chances to be “hit” by the river card (6 outs or more)
• As a rule of thumbs, you should rather bet yourself with any hand that you consider good enough to call a bet with

You should call somebody else’s bet:

• When there is an acceptable chance that the turn or river will improve your drawing hand and make it a winner
• When you think your hand is winning, but you want to wait to raise your opponent’s next bet on the turn, where the stakes are higher (watch out: the turn card may be bad for you, or your opponent may check the turn instead of betting)

You should fold:

• When your hand has little chances to be the best hand and you have few outs (5 or less)
• When the opponents actions indicate that he is holding a strong hand that beats you even if you improve (you are “drawing dead”)
• When the relation between the probability of improving your hand and the pot odds gives you a negative expectation

You should raise:

• When you think you have the best hand
• When you have a draw with 8 or more outs
• When you think that you can beat the original bettor, and by raising you can make all the other players fold, and thus you “isolate” the original bettor to play him heads-up

You will see that the various recommendations are sometimes contradictionary. This is because you have to take various factors into account, and the above recommendations are simplistic and give you only a rough outline.