Protect the top portion of the wainscoting with a hand-held masking machine. Ensure that the tape on the top edge of the wainscoting runs right up against the wall then pull the machine along slowly so that it dispenses the tape and paper in a uniform layer to protect the top section of the wainscoting. Add additional layers to cover the entire wainscoting.
Put drop cloths along the floor at least 4 feet out from the wall and drape any nearby heavy pieces of furniture with the cloths as well. If necessary, climb up on a ladder to apply a layer of tape and paper along the ceiling where it meets the wall to protect the ceiling from over-spray and paint roller flecks. Use an extra roll of masking tape to patch the paper where needed or as extra adhesive.
Paint the wall as you would normally. Roll it on with a paint roller and use a brush in corners or a paint sprayer hooked up to an air compressor if you prefer the more direct and messy route. Complete all of the coats and let the paint dry completely before you remove the masking tape and paper, as well as the drop cloths.