My advice to you:
Constantly read design blogs. You're getting into CSS a little late in the game so there are thousands of helpful tips and tricks out there.
Stay away from hacks, browser workarounds, etc.
Keep a copy of IE6 lying around and prepare to hate it with all of your life.
Utilize
CSS frameworks for laying out your design, then switch the classes over to a more semantic meaning when going live.
USE A RESET.CSS FILE. I recommend
YUI reset.
Welcome to the dark side.