Run a sanding buffer with a medium-grain sanding ring over the entire wall. This will smooth down the main areas of roughness and texture to create a flatter surface.
Run a sanding buffer with a fine-grain sanding ring over the entire wall. This will remove any smaller patches of roughness and will flatten out the smallest imperfections to create a sleek surface.
Run a shop vacuum over the wall with a brush attachment, which will remove the debris caused by the sanding.
Moisten a washcloth, and wipe down the entire wall. Allow the wall to air dry for 30 minutes.
Fill the bottom of a paint tray with matte latex paint. Matte paint will make the sanded wall appear even flatter and more smooth.
Coat a paint roller in the matte paint, and apply the paint over the entire sanded wall. Allow the paint to dry for 8 hours, then apply a second coat in the same manner. Allow the second coat to dry for an additional 8 hours.