Well I did a very QUICK job this weekend (this are my bodge mirrors got new pair in the shed)
Car currently with the black mirrors (yes thats my dads 525D to the left)

I used light grade sandpaper to roughten the surface (dont forget to wash etc to remove grease etc)

I then masked off all areas I did not want to spray

First coat of Grey primer (build up a few coats or untill you have even coverage) dont forget to wet and dry this is the surface the paint is going to go on

I then sprayed with my cars colour paint (Zinnoberrot) build up a few coats again using wet and dry 1500grit inbetween coats

I will be using clear lacqure for the real job but for this quicky I didnt
Heres the mirror with the masking removed
And the car viewed from the front see the colour coded mirrors?
This is only a rough guide im sure others will have views and ideas (as you can tell I love taking pictures of everything I do, it always comes in use