i did this to. To prep i sanded it with 360 grit to get the crappy paint off, you could use 220 as well. Then i went to a finer grit like 400 then again with 600 to remove all the scratches. After that you will want to blow it off with a compressor or whatever, then wipe it with something like final clean. That what i use, it doesnt smear the paint it just cleans the residue and anything else off. I then painted it with a single stage black enamel paint with my air brush. hope this helps
87foxstang gave you good advise. I have used the same process in the past with good results. I usually get wet/dry sandpaper,the black color. I like to use the paper wet,either with water or glass cleaner. Get it as smooth as you can and keep it clean before topcoating.
IF the part has had armorall or wd40 on it recently, you need to scrub the daylights out of it to remove all traces of silicone.there is a solvent made for this purpose.