How to Get Wallpaper Ready for Painting
Smooth out any lumps in the surface with sandpaper.
Use a 150-grit sandpaper to sand down lumps or bumps.
Rough up the surface of the wallpaper.
Take the same sandpaper and lightly sand all over the walls so that the paint will have something to stick to.
Dust (or vacuum) the surface.
Try using a tack cloth to help remove the grit.
Brush on two thin coats of oil-based sealer.
Be sure to keep each coat thin. If you plan to finish with a particularly rich tone, such as red, you might want to use a tinted sealer.
Roll on your finish coat.
Once the sealer dries you are ready to apply your finish coat (the paint).