Pretty much what gazedrop said. If you're not sure how thick the coats should be, err on the thin side. Better to do too many thin coats than too few thick ones (not only will it look better but it should last better too). It's a good idea to put on some clearcoat too (at least five coats), this is harder wearing than the color coat and will protect from minor chips and scratches (better to polish off the clear than the color).

I've painted two BMX frames recently, with varying results. The first I did quite quickly, with rattle can primer and top coat. I didn't let it cure enough between coats or after I'd finished, and it chipped VERY easily (like with a fingernail). The second one I used the same primer, but with Humbrol enamel shot through a compressor, rattlecan clear with funky metalflake particles suspended in it, and regular rattlecan clear on top. Having learned to wait between coats it turned out much better, but I didn't put enough clear coats on to cover the metalflake properly (but since you probably won't be using metalflake, 5 or so coats will be plenty).