Use the advance check boxes: If as a player you become a bit of a wizard and would like to play more than one table at a given time, that's certainly an option. But, to do so, you'll need to master the art of advanced checkbox usage. If you know what you're going to do, or would do all else being equal, you can submit your action in advance of it being your turn. Let's say there's a $10 bet to you and you're in mid-position. You may have a hand that warrants a call of the $10, but if it gets to you and after the initial $10, there's a bet and a raise, you wouldn't call with your hand as it's not looking so strong anymore. You can use the "call" advance checkbox that will make a call if that's your wish, but if there's subsequent action to the initial action that lead to your decision, you can have your hand folded in advance of you giving the hand further consideration. If you're a multi-table player, the usage of the advance checkbox becomes paramount.
Lack of Visual tells: online, there are no visual signals to indicate what a player may or may not have. An observed twitch, nervous demeanour, these things are not in view online. What happens is that players rely a lot more on the actions players make within the game. Bets are not stared down by suspicious players looking for a physical tell, but rather bets are made that are probing in nature. Continuing that line, a lot of raises are made as questions to the original raiser, more so than you would see in live poker games. It is important to be aware of betting action, historical betting patterns, and getting a feel for what your opponents appear to habitually do in certain situations. Of course, the sage player will make a situation appear something that is is not.