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Obviously, you'll need a paintbrush and paint, but for best results, you'll likely also want a suitable primer. Be sure the paint and primer you buy is intended for your purposes (interior vs. exterior; acrylic vs. oil based), and, all in all, be sure you also have:  Clean rag Drop cloth(s) (or newspaper) Hammer Latex paint (or other suitable paint) Paintbrush Paint tray (for roller) Primer (if necessary) Roller (low-nap) Sandpaper (fine grit, 180 - 220-grit) Sawhorses Screwdriver First, close the door so the hinge opens flat, allowing better access. Then, use a small screwdriver to force the pins out of your hinge.  You may only need a screwdriver to accomplish this task, but if the pin is stuck, tap the back of your screwdriver with a hammer to pop it free. If you don't have a screwdriver the right size on hand, you might try using a nail pushed through the bottom of the hinge. The shape of your door and the material it's made from can make handling a door by yourself cumbersome, difficult, or dangerous. Especially if you are painting a metal door, which can be extremely heavy. Once the pins have been pulled free from all hinges, remove the door from its frame with your helper. Make sure the area you will be painting is well ventilated, clear of obstacles, and properly covered with drop cloths or newspaper in case of drips or splatter. Laying your door atop sawhorses with the side you intend on working face up will make the sanding and priming process easier on yourself.  You can lay the door on the floor, if necessary, but this can dirty your door or accidentally cause damage. To prevent your door from sticking or freshly applied paint from becoming damaged by your sawhorse, you may want to use cardboard to pad the tops of your horses.  Sanding and painting bent over might also cause back pain.
Gather your door painting supplies. Use your hammer and a screwdriver to remove the hinge pins. Have a friend help remove the door. Position the door in your work area.