Start by sanding and the priming the door you plan to paint. Be sure to sand uneven spots until they are smooth before you apply a coat of primer for the paint to stick onto. Allow time for the primer coat to dry before you move on to the next step.
In order to prevent foreign objects such as doorknobs and handles attached to the door from being painted, cover them with painter’s tape. Moreover, it will be a good idea to slide a piece of cardboard, tarp or an old towel underneath the door before you start painting it. Use wooden shims to make sure that the door does not close while you are painting or before the paint dries completely.
To protect the hinges from being painted, clean them with rubbing alcohol and cover them beneath two coat of rubber cemented which can easily be removed when you have completed the paintwork.
Start painting the door with a 3-inch paintbrush at the bottom left corner and work your way towards the top of the door. This will minimise dripping and thus lesser volume of paint would be used. Be sure to use long, even paintbrush strokes for a clean finish.
After you have painted the bottom part of the door, paint the top left part. Start with long, vertical strokes and continue until about one third of the door is painted. Paint across the vertical length with horizontal strokes and continue in this manner until the entire door is painted.
For a clean finish, paint the top of the door vertically. Be sure not to leave brush marks while painting. Allow time for the paint coat to dry completely and then apply one more coat if required.
Finally, clean dust traces, if any, using a vacuum cleaner with brush attachment.