A few tips:
Being able to calculate odds on the fly. EX: You're holding a 7 and 8 of spades with a flop of 9 of clubs, and a 6 and 2 of spades. You're looking at 15 potential outs between your open ended straight draw and flush draw. You'll be 60% to win the hand, so chasing either draw is a good play.
Slow play the nuts. Flop quads, don't bet, let the action go around the table. Bet the turn if no one else does, but just enough to keep someone chasing their draw. And always bet the river, by then you either will force someone to fold and take it outright, or win the hand regardless.
Take breaks. Often...it's easy to get burnt out sitting in front of the PC playing cards all day. Most online tourneys have breaks hourly. Playing single table non-tourney and you can sit out a few hands, you won't be forced to post blinds.
Remember, any hand can win. Make sure you know what the best possible hand is on the flop, turn and river. If a straight or flush is possible and you only have a mid-pair, don't consider it a good hand to hold onto. Trips (3 of a kind) would potentially draw out against a straight or flush by either the board pairing giving you a full house or maybe even quads (4 of a kind), but that is a judgement call based on the price you'd be paying to see the turn/river.
And also, poker is the only true form of gambling where skill actually comes into play as often as luck. Picking up the art of semi-bluffing (when you have a relatively strong drawing hand) is a valuable acquisition.
Good luck and enjoy. :iagree: