When playing Texas Holdem, playing your opponent will become just as important as playing your cards in many games. At the higher levels, playing your opponents will become more important than your cards.
The below video goes over the four common player types. Many of your opponents at the lower limits in poker will fall in the loose passive or in the tight passive style. There are times that you will find players that will actually play a different style than normal to throw people off of their game. Gus Hansen has a big image of being extremely loose aggressive, but in reality, he is closer to tight aggressive. It is the times he will deviate from that strategy that has given him that image.
You will also find instances where you will want to switch up your playing styles, even within your hand. For example, if I am in a game that has a lot of loose passive players, sometimes I will play a loose aggressive pre-flop game and then turn on the afterburners after the flop.
The key to being able to pick up on player styles is focus at the table. There are many players that will sit at the table, and they are totally focused on the hand while they are in it. After they fold, their mind and attention is anywhere but at the table. This is a detriment to their game as they are missing out on information that can help them later. Granted, in some games, you will pick up the information you need quickly, but that is not always the case, especially in a NL game.
Take a look at this video and keep these concepts in mind the next time you set out to play poker. You may discover you need to adjust your game to help increase your winnings. Good luck.