Painting over wallpaper is fairly simple with a few guidelines to follow.
1) The main guideline is the primer. Use a shellac based primer. This is a smelly proposition but the shellac primer will stick to the wallpaper and seal any stains.
2) After priming, and ample drying, some of the wallpaper might come loose or bubble. Large loose areas can be cut out and drywall mud applied to level out the area. Priming will also produce an evenly colored background that will show any defects in the wall and make it easier to see the wallpaper seams. Apply drywall mud to any areas that you don't like.
3) Re-prime any repaired areas then you can paint with your favorite color.