Using a pole sander fitted with 120-grit paper, sand the walls (make sure to wear a dust mask). Sweep the sander side to side as you work your way from the top down. Apply medium pressure, and take care that the head doesn’t flop and gouge the wall. Change the paper whenever the grit gets clogged with dust.
Remove bumps or drips on painted molding with a scraper. Then, using a dampened coarse-grit sanding sponge, rough up the surface. Keep a bucket of warm water nearby, and continually rinse the sponge. Finish with a dampened fine-grit sponge.
Using a wet/dry vacuum, clear all the dust from the walls and trim. Wash the walls with a sponge, using warm water and dish soap. Scrub greasy or waxy spots. Wipe everything down one last time with clean water