I am not a painter. But if the frame already has a decent surface finish (which the clearcoat should be), I'd save me the hassle and just rough it up with fine sand paper. If you can get rougher scouring pad, that might work, too, and is way easier to handle wet.
If you want the paint job to last a while, finish with a 2-component top coat.
You could look for ETOE on yt to get some ideas. He shows how to do a lot of cool paint jobs, awesome effects and stuff, on the cheap (rattle can jobs). The first few minutes might be a bit cringe (with his very German brand of English, all the overacted enthusiasm and sometimes suuuper cheesy dance tunes), but you get over it and the videos are rather informative.