Hi mate,
use good old wet and dry, and sand back onto the good paint to feather the edges, you may need to put a skim of filler over the really rough bits, mask off properly and use a good quality primer and then your chosen spray, lots of thin coats are best with lots of drying time in between and I always like to flat the final coats with super fine wet and dry (wet, using a little soap) then cut the final coat of colour, remember that metallic paint needs a laquer which can take an age to harden.
I am sure there are more comprehensive posts, but thats about it, just take your time, a home job will never look as good as a paint shop, but it can be done quite well.
Good luck
Fram.