The one thing that I cannot stress enough about playing NL cash games online is to TAKE NOTES!!!! Document what kind of hands the raiser shows down, what they play, what they call with, and HOW they bet. If a player will make pot sized bets when hes holding a big pair, but check when he hit his set, its pretty easy to let your hand go. If a player frequently check-raises on a bluff, you can call him down with less than marginal hands. If a player that normally calls,folds,raises quickly, but all of a sudden he takes his time before he raises, you can be sure hes trying to decide how much to raise his big pair. These aren't absolute rules, but just a few tips on how to read opponents.