As you play hands, other players begin to form an impression of you. This impression is called your table image. Being aware of your table image can help you choose the best play. It works most to your advantage when you play in a way that appears consistent with your image, but actually is not. For example, if other players view you as a tight, aggressive player who waits for premium hands, you will have an easier time bluffing. On the flip side, a player with a loose passive image will have an easier time inducing bluffs from aggressive players.
If you make the same play all the time, it will start to become part of your table image. This can work against you. For example, if you constantly steal blinds, other players will begin to notice. They will suspect you of raising with any two cards when in a possible steal. If you continue to steal at every opportunity, you will be trouble.
You could try to oscillate your strategy so that your actual strategy and your table image are out of sync. Unfortunately, different players will have a different image of you, so this is not really possible. Your best bet is to use a mixed strategy, where you randomly select from different options in order to confuse your opponents.
One type of image you generally do not want to project is the image of an expert player. Other players will watch you more closely and work harder to beat you—definitely not something you want. You want the game to seem casual, like you are just playing for fun. In fact, you want to encourage other players to think that way. If you give off the impression that you take the game seriously, they'll start to take it seriously too. In general, avoid talking about the game, explaining how to play more correctly, or criticizing someone for playing poorly.
In online play, image is less of a problem as most players are not paying close attention to the other players anyway. In live play, table image is more critical. Avoid the look of the stereotypical shark. Don't wear sunglasses. Cultivate the image of someone who gambles only occasionally and is just here to have some fun. Consider a Hawaiian shirt.