Some of the Online Texas Hold'em Poker Strategy.
Table Selection - By far the most important skill is table selection, so it ranks better than #1. It doesn't matter how well you play if you are always picking the games with no fish where even an expert can't beat the rake. If you play fairly well, you won't lose much to the better players, nor win much from the slightly inferior players; it's the fish that count. Most of your income will come from a few very bad players.
Mistakes and misfortunes when beginning is a normal thing - Having gained good practice with playing for free you will definitely want to play for real money. But don't hurry up and bet hundreds. Nobody makes success at once, except of those legendary heroes, whose personalities are uncertain and I bet fictitious. Begin from low amounts and don't be afraid to lose and don't get upset if lost - learn from your mistakes, and better write everything down to have your own "tip list" in pocket.
Opponent assessment - Your goal is to stereotype each player, as well as to note particular idiosyncrasies of the individuals for use not only now but in future sessions. As play goes along, give yourself a running commentary of the events. You must make a lot of mental notes based on this, and you must do this even when you're not in a hand, because in addition to being useful during a hand. It's useful for later hands. You want to see the frequency with which a player sees the flop, the frequency with which a player defends his blinds from raises, and the hands player just calls with, raises with, cold-calls with, and open-raises with. This in conjunction with narrowing down the hands above will often give you a good idea of what's going on even when there is no showdown.