If you really like Flea's style and want to learn some good,
fast slapping/popping bass lines, check out some old (pre Mother's Milk) Chili Peppers recordings. Blackeyed Blonde was the first song I figured out how to slap by myself and it's a very rewarding feeling. Also check out guys like Victor Wooten and Bill Dickens. They've got distinct slapping styles as well. "Take the Power Back" by RATM is a cool slapped Timmy C. bass line, if you haven't already heard it.
Slapping/popping does take some work to get down, but once you get it, well, you've got it. Just remember to keep your thumb and wrist loose and let gravity do the rest.
Everyone does it a little different, but these are the guidelines I started from and eventually I found the method that worked for me. Also, remember to keep your bass at a playable height. There are some advanced slapping techniques that you can't do with a bass at your knees. Private lessons (if you can afford them) are, in my opinion, the best way to learn how to play because you are learning from someone with knowledge and experience that can explain everything in sensible terms. Hope I was some help.
