I left the flares on and used index cards, masking tape & newspaper. I inserted the index cards between the flares and the body where I could, masked off the rest and covered any other areas I was worried about over-spray with newspaper.
I scuffed the flares with a green scrunge pad, and wiped down/degreased with rubbing alc'y and a rag. After it dried, I put down 3 coats of Krylon Fusion.
I used virtually the same drill when I refreshed my rusty door handles. Except I used actual sandpaper and Rustoleum rattle-can bedliner.
What a difference! YMMV, and invariably will...