Well, the obvious tip is to try to paint the rims with not tire or tube on them. I started with 4 old wooden spoke 21" spokes and 5 rims. Took off the old tires and tubes, sandblasted the rims and while my son was sanding and inspecting the wooden spokes and staining them and spar varnishing them, I cleaned up, inspected and painted the rims. As I mentioned, I used the silver and it came out too "bright" I sprayed one coate of red oxide primer and then hand brushed the dull aluminum shade paint on them, two coats to insure good coverage. Let dry and cure a week if you can as you will put some scratches on the rim with the rim spreader or wood blocks or whatever you use to mount the tire.
Other than the shade, I'm happy with the way they came out.
