How to paint panels

Introduction

Wear safety glasses and old clothes in case of paint splashes. Protect your hands as you will be dealing with chemicals.
Tape areas such as windows, roofs, chimneys with painter's tape. Remove the switch plate covers from the walls.
Clean the panels with trisodium phosphate (TSP). Mix it with water following the directions on the bottle. If the panel is particularly shiny, you may also need a degreaser. Fortunately, you can purchase products that include both TSP and a degreaser. This step is very important, because if you don't do a good job of painting, the paint will never stick to the surface of the panel.

Fill in all bumps, nicks, and other irregularities in the panels with a putty knife and putty.
Sand the panels with 120 grit sandpaper to roughen the surface so it will accept more paint. Really apply a lot of pressure. Use a sticky cloth to wipe off sanding dust.
Apply an oil-based bonding primer to the panel with an old brush or roller, something you're willing to throw away, because primer is quite difficult and messy to clean. If your panel is darker, use two coats of bonding primer. I recommend light gray primer because almost any color can go on.

For a "California" style look, use a soft vanilla latex over the primer, applying with a roller.
To add a striped effect on top, mix a little more of the same latex paint with enamel. The more saturated you want your color to be, the more paint you will mix. Load your brush with the paint/glaze mixture and drag it in one direction to leave the striations. You can also use texture paint on the panels.

The panel painting process is rigorous and time consuming, but the results are amazing. Just consider this example of a family room before (Image 1) and after (Image 2) its panel renovation.