The easiest way to make money online playing poker from the US is to learn the short stack game for NLH. Virtually everyone will tell you that you should always buy in for the maximum amount, but that is fallacious thinking, as buying in for the maximum amount leaves you and your stack open to the maximum destruction. This is also critical to learn, as at some point, you are guaranteed to play the short stack game via what is called the effective stack size because the game is played for table stakes. This means that the only stack size that matters is the smaller one, as the larger stack cannot force the smaller one to play for money that he or she does not have at the table.
Thus, the smaller stack dictates the play. This also means that the smaller stack has the leverage to put larger stacks all in in more uncomfortable situations and play for dead money while the remaining larger stacks in play can still push each other out of the pot. This gives the smaller stack a mathematical advantage, which is expressed by the term “short stacking”.
Though you should learn eventually to play all the stack sizes (short, mid, and full), particularly if you are a tourney expert, you should literally spend most of your time learning the short stack game. Most sites have banned the practice because the advantage is just too strong, yet at America’s Cardroom and Global Poker, as of this writing, you can buy in to cash game tables for just 20 and 25 big blinds, respectively, and 30 big blinds at Ignition Poker. Buying in for an amount that is 40 big blinds does not convey an advantage, though I would hasten to say that it is still vital to learn a mid-stack game en route to eventually buying in full.
For more information, you should follow the Short Stack Hero blog, as well as purchasing the book Automatic Poker by Jimmie James Jr. (and following his blog), which you can find on Amazon. Should you desire a primer on short stacking in pot-limit Omaha, buy the book Pot Limit Omaha: Understanding Winning Play by William Jockusch.