First of all I want to talk about Rake Back. I'm talking about this first because I missed some opportunities when I first started playing poker online. In every hand of poker you play online you contribute to a side-pot which Is called Rake. Rake is the money the house gets from every hand played. As a new intensive to play online poker a lot of sites offer you a deal to get a percentage of your rake paid back. If you like me and play a 5-6 thousand hands a week then this can easily mount up to $ 100- $ 150 by the end of the month. Also if your playing in difficult games this helps push up your edge.
Another thing I recommend is getting some sort of tracking software. The main two are Hold-em manager and Poker Tracker you should find these easily by doing a Google search. These software's allow you to track how many hands you have played and various statistics about your play and the rest of the people at the table. This information is invaluable if you play many tables at once as they also display the statistics on top of the table you are playing on for easy reference.
If you are going to play a lot of poker online its also useful to get a second monitor this allow you to do a two things. If you want to you can play more tables at the same time as long as you can keep up with the action. You can also do the other thing you need to do on the second monitor while keeping up with the action. I personally have two Acer P193W 19 inch but if you can afford bigger go for that.