The first thing to do is to have the proper tools on hand. There are 2 methods to complete this project, spray painting or using a paint brush. Spraying is quicker and leaves a slick finish, but it calls for more expensive equipment.
When using brushes, never skimp on price. A professional paint brush can be had for $10 to $20 USD. Oil-based paints call for brushes labeled as such, and latex brushes should be used for water-based paint. Always use a tapered brush for maximum control.
Remove all Door Hardware and then Paint
A key to a professional finish is to take the door down and then remove all hardware; the hinges, door knob, latch, etc. Trying to mask off these areas and paint around them is both time-consuming and sloppy.
If the door is new; it should be morticed and have the hole for the doorknob assembly and strike cut now. Then it will need to be primed and lightly sanded. Existing doors should be chipped if needed, sanded smooth, primed in bare areas, and then lightly sanded. The key to this step is to start with a smooth finish because any surface irregularities will be magnified further on down the road.
Next, it’s time to apply the paint. In almost all cases, it will be necessary to apply at least two coats with adequate drying time between coats. If more than 2 doors are being finished, the labor time payoff is on the side of spraying. If brushing with glossy latex (most situations), a superior finish can be achieved by adding some Floetrol to the paint. This product is a conditioner that will eliminate brush strokes.
Plain flat doors may be rolled to save time but always brush it down to eliminate any “texture” left by the roller nap. Other doors are usually made up of an upper rail, lower rail, side stiles, and mullions (the framing members), and the panels (the inset parts).
The painting order of operations boils down to personal preference, but many painters begin painting the panels, then the architectural details of the rails, stiles, and mullions, and then finishing off with the remaining flat areas. Virtually all edges will leave a bead of paint that must be feathered off which is why this method is preferable.