Its worth getting some proper solvent to degrease the surface properly before painting. Gets rid of any oily finger residue etc.
Very simply:
Prep it with 240-400 paper,
give it a few thin coats of high-build primer.
Flat it back evenly with 6-800 wet & dry paper. Make sure its perfectly clean/dry and go on with the top coats.
Theres lots of advice about spraying technique online
