Poker is game of observation as well. Determine the style of play for your opponents oserving their moves. This is the key to winning. The moves which a player chooses make for theirs style of play so keep notice on how they think and act.
Styles: tight and loose, passive and aggressive players.
Tight and loose players
We tell them apart by their hands. Tight players play few combinations, and loose player play many.
Passive and aggressive players
The way in which we describe a tight or aggressive stlye of play. Passive players mostly avoid competing for pots out of fear of losing a hand and they easily forld. This is why you can bluff them more easily. Aggressive palyers raise the pots more often and rarely just call as they gladly risk their chips.
Observe your opponents. Your opponents will one of the following traits. First set if it's a tight or loose player (if he plays a lot of hands he is loose, if he folds a lot he is tight). Then compare if he plays passively or agressively (passive call more while aggressive ones raise more) and adjut your game.