It’s easier to achieve a professional-looking finish if you take the time to remove the locks and knobs. You can tape them off and paint around them, but it’s not the best approach. If you’re considering new hardware, now is the time to get it.
Clean the door and use a palm sander to roughen the flat surfaces of existing paint (Image 1). This will help give the primer a better surface to adhere to. You may have to hand sand in the crevices and around the trim (Image 2).
Wipe the entire door clean with a dry rag to remove dust (Image 3).