I start by getting the wood as dry as possible, When I am painting a small object I heat it with a heat lamp and dry every surface inside and out,when Painting something large I that is made out of wood I just use heat lamps and keep moving them until I have heated the whole thing. I heat it to the point that it gets hot enough to hurt if I touch it.I have found if I dont do this all The joints print through about a week later, I even built a forced air heater to attach to the speakers I build and let it run for several days,It forces hot air in the bottom and out the top,Then I cover the whole surface with a primer,then fill the entire suface to be painted with thinned body filler, I thin the filler with "Plastic Honey",
Then sand and reheat the whole thing before sanding down to 600.
I do this to get the surface to stay flat and to all the seams from printing through. If I dont do this all the larger grained surfaces swell up and become very wavy even if you sand them down they seam to show up later and end up looking like painted wood. This just the way I do it,
Aaron