2slow,
I'd put down a primer coat too. Not only does it give your paint a constant color underneath, it will help the paint bond better. Once you lay down the primer coat, wet sand it with 400 grit paper to give you a smooth surface. If you have to, lay down 3-4 coats of primer. This is one thing primer is designed for, to help smooth the surface and fill in any small defects, and to give your paint a better surface to bond to.

If you want a good finish coat, after the primer lay down 3-4 coats of your "color" and wet sand with 400 grit paper between each coat. This will give you a final coat that looks like it has "depth" to it.

Hope this helps.

Ken