How to Read Tells in Online Poker

Insta-Plays
One way to identify a player's tell is to observe the speed with which they make a move. If they make a play immediately (also called an "instant-play"), that may be a sign that a player is confident that they have a good hand. Your goal and strategy then will be to break down this confidence and force players to second-guess their decisions.
Tanking
If players "tank," or play slowly, this hesitation may also provide some insight into their current hand. Often, it may be a sign that they have a mediocre hand and are ruminating on how to play it. Tanking is also frequently a sign that a player is working up a bluff, so pay close attention to what a player does after taking a lengthy amount of time to make a decision.
It may take at least a few rounds to determine what a player's pacing indicates about his or her hand. In online poker, you have to pay close attention betting to your opponents' moves and styles, just as you would in a traditional poker game, in order to get a sense of their rhythm and their methods.