Originally Posted by xCEZRx
Yea taking notes does help me concentrate but some days I just can't spot anything worth writing down.
Yea happens to me too, still not mastering this art.
Assuming you don't have a HUD, write down a rough % of the amount of hands the guy is playing pre-flop. Write down another rough % of the amount of times he is entering the pot with a raise. Those are the 2 most important things to know about every player because it defines their range.
The next most important thing (IMO) is what do they do if they are in the blinds and you raise from the CU or BU. What % of the time do they fold? And when they don't fold, do they 3-bet or simply call as a defense? What do they 3-bet/call with?
When they are post-flop, are they aggressive or passive? Do they raise most of the time, do they simply check/call? Do they set traps? Do they slowplay high flushes, the nut straight, or sets? Do they fold to a c-bet on the Flop?
And if you end up going to showdown, write down their hand and how they played it. I usually make a quick summary of the interesting hands they played and how they played it until the river. I've watched some pro streams and noticed that they actually copy/paste a hand history they shared with that player into the note field (you actually see the "Seat 1: x, Seat 2: y"). Then they go down to the interesting part and see how the guy played that hand.
But I prefer a short summary like "Called pre-flop 3BB raise with 44 UTG after limping, check/called set until the River with a +/- dry board, check/shoved River" over this approach. If I have enough hands on him then eventually I delete all this history and place a general range there. For example "will call preflop from any position with pocket pair; will check/call with a monster until the River in a dry board, then check/shove, and if the board is wet will bet the pot on the flop, and shove on the turn".