I consider myself a pro and it comes natural to me, I know what my opponents have at all times.

Seriously though, I think it might help you if you go to the HH section and plough through a bunch of those and do the detailed analysis like "if he had AK, AQ, he would play this like this, if XX then like that, if YY then I would expect something else" etc. There you can take the time to contemplate about it, which you don't have in real games.

Maybe noobish, but I don't think I do much more than "if he plays little hands, it's probably a tight range of top hands, if he plays loose, he can have anything". I look more at the betting pattern to tell me how hard (if at all) he hit the flop - so in a way let THEM tell me if they have a good hand. Dunno if that makes sense.

Another important thing is the continuation-thing. If you put someone on a bunch of hands on the flop, and then he starts "repping" a hand on the turn that wasn't there, something is probably up. Like if the flop is K72 and you know he would bet if he had the K but he checks, and then the turn is another K and he bets.. it's probably a steal b/c he won't have the K. Stuff like that.