I need help painting my WW duckbill spoiler (non cf)

It has like semi-gloss black paint on it right now and needs to be repainted.

What are the steps/procedures?
Do i haft to primer it?
Sand the paint thats on it off?
What do i do to prevent orange peel?
What grit sandpaper?
Ill be using paint out of any aersol can..
Is there any good name brands?

Thx