I bought Duplicolor's wheel paint and it works great! You will need atleast 2 cans of it, I also bought their clear coat for it.
Buy some high grit wet sanding paper too.
Start by cleaning the wheels with dish soap. Wash them until they look spotless.
Then start your wetsanding. You aren't trying to take the stock wheel paint off, just trying to create a surface for it to stick to. You are basically just taking off the clear on the wheels. Go over the whole wheel thoroughly.
If you are planning to fix curb rash with some body filler then this would be the time to do that.
I didn't use a primer on mine, some say you have to, but I didn't and I believe duplicolor says you dont have to. They came out good for me but might depend on the color, I used the gunmetal color.
You want to have some index cards (only if you are painting with the tires on) and stick them in between the tire and the wheel all the way around. You can block off more of the tire with some news paper.
Start with light coats, you don't have to completely make it black (or whatever color) in the first coat. You don't want to have runs. I did 4 coats per wheel. Then 2 coats of clear. Let them drive for a few hours before putting them back on the car, also wait a few hours after they are on to drive on them. (Don't want anything to stick to the paint.)
I did it on my 6. Ugly looking tires take away from it but you get the idea. I didn't paint the center caps because I didn't want to tape the "M" off but I liked them standing out from the wheel.