Remove all furniture and loose rugs from the room. Cover all wall-to-wall carpet and set up a work light.
Sand down all wallpaper seams and pre-existing plaster patches.
Roll on a heavy coat of primer. Begin at the top, left corner of the wall and work to the right, or start at the top, right corner of the wall and work to the left. Brush out all primer runs or ridges. Let the coat of primer dry according to the manufacturer's directions.
Hold your spackling knife flat in one hand, and move it over the wall. Apply the spackling compound with very little pressure on the knife. Spread spackle over the wall texture as well as any dents and dings. Let the spackle dry according to the manufacturer's directions.
Check the wall for smoothness. Sand any visible rough spots. If you can still detect texture, or you desire a smoother finish, apply another coat of spackling compound and let it dry thoroughly.
Sand the surface of the wall prior to applying the finish of your choice.