prep.. you're going to have to take some sandpaper to where you will paint to make sure the paint will stay..
if you live in an area where you get salt for snow.. u'll need to touch them up every year b/c the salt eats it away.... but it looks good when it's done.. not too much paint or you'll have to wait until it fades a bit to match...
but i've been doing it for 3 years and love it