1) clean the surface with vinegar or something to cut the grease and dirt. 2) Lightly sand the surfaces of the doors in the direction of the grain only enough to ruff them up for paint adherance. 3) I like and use Zinzer BIN primer. use any good primer and cover the doors. 4) remove all hardware or masking tape off. 5) If the doors are paneled doors begin with the enlays and work out. Apply several coats of a good reputable paint purchased from a paint store. 6) you might want to do like many people do, pull the door off the hinges and paint them laying flat on saw horses. I like doing them while hanging, its easier and you don't have to worry about springing any hinges.