See also Hold'em: Protecting Your Hand
When you play a hand, your opponents will want to use some of the techniques to analyze your play and try to read your hand. You, in turn, want to make this process as difficult as possible for them. For most players in live games, this means cutting down on any physical tells - wearing dark glasses, remaining quiet, not jiggling their knees or tapping their fingers and the like.
One way to tight against being "read" in this fashion is to make sure you diversify your betting sequences. Simply put, you need to make sure that any betting action by you is capable of multiple interpretations by an observant opponent.
Let's consider a concrete example. You're in fourth position at the table. There are three folds to you, and you pick up

You make a raise to three times the big blind, and the player one off the button calls. The button folds, as do the small and big blind. The flop comes

Keep that thought in mind, and now let's consider the situation with a different flop. This time the flop comes

Most beginners and intermediates in no-limit cash games follow an obvious poker strategy. In the first case, they bet since they have top pair and top kicker, and they want to make some money on their hand. In the second case, they sometimes make a continuation bet, to pick up the pot without a fight, and they sometimes check.
Notice that someone who plays like this is easily exploitable. If they bet, they may or may not have a pair or better. But if they check, you know they missed the flop, and you can probably pick up the pot with a strong bet.
That's too much information to give an observant opponent. It won't matter much if you're at an online table full of strangers, or if you just sit down in a live game for an hour or so. But if you're in a regular game or playing a long session, you have to do better. Let's see how you can.
One simple method would be to bet half your hands, whether you hit the flop or not. In this situation (where you lead off preflop with a strong non-paired hand, and get called), you will make a pair or better on the flop about 30 percent of the time, and miss the other 70 percent. If you bet half the time no matter what happens, then your opponents won't be able to dedeuce anything from your post-flop action. If we look at a sample of 100 such hands, you'll bet 50 of them, which will consist of 15 occasions where you made a hand and 35 where you didn't. The same percentages will apply when you check; 15 times you'll actually have a hand, and 35 times you won't.
Of course, there will also be hands where you started with a strong pair, so that after the flop you have at least a pair, and perhaps two pair or a set. These hands you will also sometimes bet and sometimes check, making your post-flop distributions stronger in both cases.
The exact percentage of time you choose to bet and check in each group isn't terribly important. (It's highly dependent on the prevailing style of the game you're in.) No one could ever observe you closely enough to figure out what these numbers are in every case, and in fact no good player has rigid percentages to go by. The important idea is that each betting sequence has to contain samples of each hand type. If you check after the flop, your observant opponents need to know that your action may indicate a weak hand, a medium hand, or the nuts. The only way that can occur is if you rigorously make sure that you sometimes take every possible action with every hand type. (Exception: Don't fold the nuts to vary your play! There are other obvious exceptions as well.)
This strategy has multiple good effects. First, your opponents have great difficulty reading you. They've seen plenty of examples where your actions were the opposite of what they expected, and now they're not confident of their ability to put you on a hand.
Second, your opponents lose interest in playing marginal pots with you. If they get burned too many times, they just don't want to play anymore.
Eventually, they start to play passive, tentative poker, or its evil twin, crazy-aggressive poker. Either of those poker styles is money in your pocket.
