I flipped through a couple online poker books at Barnes & Noble and they seemed pretty lame. Many people say Doyle Brunsons Super Systems is the best poker book.
I play every day at Party Poker. I only play NL Holdem. Here is my advice:
Take notes! Its seems silly at first but after you play for awhile you see the same people and its nice to know how they played.
I also put "fish" or overly aggressive players on my buddy list so I can have an easy mark. I keep notes like how much they bet with certain hands and how much the blinds were when they did it....if they are easy to bully etc. I mostly just play the single table sit and gos. I will take a few minutes a day a go through the sit and gos with three players left and put in a note like 6/22/04 $50/NL Top 3.....after a while you will see the same players winning often and I might avoid sitting down at a table with a bunch of good players. I only play $50/100/200 sit and gos. The $5-30 are really loose and I think a waste of time.
I also think that the higher the stakes the looser you can play. People playing 100/200 games play TIGHT.
If you havent seen them,
www.pokertracker.com and
http://www.pokerinspector.com are pretty cool.
Btw, Ive played at almost all of the poker rooms and I like Party Poker the best because there are constantly tons of people playing and its fast and easy to cash out.