As several people above have mentioned, it's all about the prep. You will need to sand and primer if you want any kind of decent result.

Yep, Ken is correcto mundo. Sand and prime. I didn't prime. I sanded like a mofo though! I had a pretty good result but I certainly didn't take my time and do the prep I should have. I did about 8 - 10 coats and sanded in between each of course. Seriously..... read the whole thread from that Charger dude. There is every bit of information you could need on there. It takes ages to read but it is totally worth it and you learn HEAPS about painting.