time to act/bet amount/pattern/amount of hands played/your instinct there are lots of ways to get a slight read but online there are alot more variables, as far as freerolls 90% of this goes out the window(study bingo and coin flip odds) but if u get up into some higher stakes where the level of play is greater then the main thing id say would be pay attention to there bet patterns, one thing is if they arent in alot of hands, chances are if they bet/call/raise they got a decent hand. of course this is only my opinion which will be different from other players