First thing you should do - watch your time at the table. If you are fully involved in the game and don't notice anything around - beware, simple playing can become an addiction! And you'll find yourself in the street without a nickel on your account. Thus, to prevent it, place a watch or a clock near the monitor and limit your playing. When the time is out, stop playing - or t least play the LAST hand and quit. Also, don't lose control over your money - they are real not virtual. Just remember it.
Next tip I'd give you is to vary your play. Always remember the golden rule of any poker game - and gambling in whole: play like you would play if you knew your opponents' cards, and don't give them a chance to predict your next step. It doesn't mean that you should fold all good hands and raise preflop with trash combinations. Play a couple of garbage hands and fold some good ones. And don't be too aggressive - you will probably lose.
Choose the table where the players are equal to you. Don't ask for losses - if all are more experienced than you are, then you'll simply lose all. If all are objectively weaker - then it's no interest, until you want to make easy money.
Take notes during the game. Tracking of opponents' actions is vitally important here. Most of the people have the strategy and style of playing which doesn't change in long-term period. Thus here your notes will help to disclose their hints and develop your game against them. Don't ever read book or distract yourself from the game when you folded during the preflop - you can miss the important features of the game and other players' tactics. Be very attentive and notice all small details during the dealing and playing process. Don't think too long.
Last tip - read poker bibles and remember that play-money games are not the same as real-money table. Observe other players' game, train and you'll reach the heights! Good luck!