Its pretty much been said before, but I'll ahead and throw in my 2 bets.
-Preflop, try and find a range of hands and how much they usually bet with that range of hands. For example:
a) 22-66 = 2.5x BB raise
b) 77-JJ = 3x BB raise
c) QQ - AA = 3.5x BB raise
-On the flop, look for things like:
a) Do they/how much do they C-bet when they hit?
b) Do they C-bet when they miss?
c) How do they bet if they flop a monster [set, straight, etc]
d) How do they play if they're on a draw. Some players like to play draws aggressively, some players like to back off and play it safe.
Also, look at the hand history as well. You dont have to memorize bets as you play, you can always check the hand history. Read how much and how they bet in a particular hand. Then look at similar hands and she how they compare/dont compare.
And as stated, dont fall into a pattern. They way you player AA shouldnt be different from the way you play 22 to the point its obvious. Mix, mix , mix.