After You Fold...
One unique aspect of poker is that you can drop out of a hand, invest no further money in it, but still watch the play in action. This is critical. In poker, you are afforded the opportunity to watch your opponents play their hands. If you're lucky, you get to see their hands and work your way backwards to match what the player was holding with how the player played it.
Here are some examples. If you see that one of your opponents was dealt a strong hand right off the bat, but didn't bet it as such, then you know you're either dealing with a passive player or a player that is willing to slowplay the occasional strong hand. If you see that one of your opponents was dealt a mediocre hand and bet it strongly, then you know you're either dealing with an aggressive player or a player that is willing to bluff or semi-bluff the occasional mediocre hand. Over Time
However, these observations apply to single hands. You'll not likely form strong player profiles from only watching a handful of hands. You need to keep your eyes on the action when you're in the hand and especially when you're not in the hand. Poker rules let you sit and observe your opponents to collect as much pertinent information about them as you can. In the first example above, if you catch two or three instances of the same player slowplaying decent hands, then you could very well be dealing with a passive player. Watch it, because you don't know what a passive player has. Check with your drawing hands, and bet and raise with your strong hands. He'll stay in against you, but won't make it expensive for you to chase your hands. You've started to develop a strategy in how you will deal with this player. And that strategy was borne of observation. Be careful with players who are advanced enough to alter their style if they think that you are catching on, or if they think they're being watched.
Even the worst players can alter their style, so keep your player profiles flexible enough to adapt. However, in the face of an uncertain decision, it's better to use information you've collected than to base it on no information at all. Conclusion
This parallel works for me, so I hope you like it. When Samurais had to undergo meditation training, their masters would walk around the room with canes. If they thought you were sleeping instead of meditating, they would whack you across the head with the cane to wake you up. The point: there is a fine line between meditation and sleeping, just like there is a fine line at the poker table between concentration on observing the action and "zoning out" because you've folded from the hand and couldn't care less who wins the pot.
Keep your eyes on your opponents, and study them at every chance, particularly if you've folded. Build your player profiles, use the profiles to help you make on-the-spot judgments, and adjust your profile as the player surprises you with a move you weren't expecting. It may come down to probabilities (ie. about a third of the time, he's semi-bluffing when he raises). That's fine, too. In fact, we'll talk about the role of mathematics and bluffing in our next and final installment of this series.