You may or may not have heard of defining the range of hands an opponent could be playing. Well even if you have, I'm going to cover the basics anyways.
Basically, defining a player's range involves deciding what cards you think that they would be playing based on their betting pattern and history (at least what history you know). For example, if they're a tight player who bets 5 times the big blind preflop, then they make a pot-sized continuation bet on an ugly flop of 4d-7h-2s, you can reasonably assume that they were holding a big pocket pair preflop, or A-K at the worst, and still think that they have an advantage based on the flop.
In any case, a lot of beginning players make the mistake of only thinking about an opponent's range when they are actually in the hand. Right after folding, they quit paying attention to the game and go back into zombie mode. And this is perfectly fine - if you're looking to be an average grinder for the rest of your life. However, if you want to improve, a much better idea is to practice defining an opponent's range, even when you're not still in the hand.
Doing this is easy: you just need to watch your opponents after folding, and try to make range assumptions based on the betting patterns that they've displayed. As you continually do this, you'll gradually improve at figuring out other players' ranges. And the only real difference between this and when you're actually in the hand is that the feeling of having money in the pot is taken out of the equation. And this might be a good thing since you can think clearly.
So next time you fold a hand, don't just go back to creating a music playlist or reading sports scores; instead, focus on the game and try to figure out the range of cards that each active player has.
