First I sand the board down with a fine sandpaper, just to make sure there are no little imperfections, and I have a nice surface to start with.
Finally I spray the whole thing with a krylon clear gloss finish. I give it 3 or four good coats to protect the painting and give it that shine. This clear coat really darkens the blacks and brings out the colors too. After that is dry I rub the whole thing down with a super fine (600 grit) sandpaper very lightly, just to make sure its nice and smooth.
For a look at the final piece check out my website.
Now grab some paint and a blank deck and see what you can do!