I haven't yet posted about poker, but since it's my other passion (besides infosec), here is an article about observation. The concept of JDLR ("Just doesn't look right") is described and examples of observation are outlined. What's of most interest is the following paragraph:

"In any occupation that involves repetitive motion, the person develops learned motor skills, things that he or she doesn.t have to think about doing that are the same over and over again. What about when, as you are watching some veteran dealer on a game, she hesitates halfway through picking up the losing bets, or makes some unexplained flub like dropping chips? That should be enough to cue the Investigator that this dealer is thinking about her motions, and she needs to be watched very closely. He might find she's just having a bad day, but she might be paying the rent from the casino's pocket."

This is what we call a "tell" in poker. Anything that deviates from the norm because the player has to consciously think about the action should be a trigger to the astute observer. This can be extrapolated to online play as well. The player who habitually bets within seconds when he has the goods all of a sudden hesitates to the max time limit then raises. Most likely this is a bluff (and a poor one at that).

Watch the patterns, watch the norms, analyze for deviations from that norm.