Strip the door to remove any existing finish if you plan to restain or repaint it. Sand the whole door and make sure it is smooth and free of splinters.
Remove any hardware you do not want on your door, such as handles and door knockers. Examine the door for doorknob holes left behind, and decide whether you want to keep them. Trim the door with a table saw to get rid of these holes, if you like.
Find the center of each door corner with a carpenter's square. Remember to accommodate the width of your table legs. Mark these locations with a pencil.
Predrill holes that match the size of your leg screws at each mark. Screw on the table legs and make sure they are tight but straight. Paint or stain your door table as you wish.