well getting a nice finish is difficult, I had to do it twice, and if you look closely you'll see the finish I got is not that good... I didn't follow the rules I think the layers of paint are too thick. Maybe I'll do a third time some day...
I had some reading about the subject.
In many forums the say :
first you need to sand paper the surface you want to paint, wash it to get rid of dust, dirt etc
then apply a primer sand a bit
after 3 thin layers of paint (sand a bit before doing each), you have to wait at least 1h between each layer to let the paint dry properly.
and finish with gloss (some people do 2 layers of gloss)
you can find the primer, paint and gloss in spray
In my opinion it is important to use good quality sprays and very thin grip sand paper.
there are some good tutorials here
http://www.360-hq.com/xbox-tutorials-70.html
http://www.instructables.com/