In order to blank out and finish a drywall, you will need the following: a large putty knife and mud. You should begin at the top. Lay on a thin layer of mud. Put a little on your putty knife. Place your putty knife in the crevice, where the ceiling meets the wall and pull it down. Repeat. Do this, until you cover your working area. Then, go back over where you started and feather it. You will need to smooth it and even it out, without distressing the area that you did first. When you finish the upper part of the wall, then you should do the bottom part. Work your way around the room in that manner. Be careful not to leave lap marks. Allow it to dry. When it dries, you might have to do a little sanding.