Dampen a clean cloth and wipe down the section of your door where you will be painting the number. Getting all the dust off before you begin helps ensure that the paint sticks and that the finish is smooth.
Type the number in a word-processing program. Enlarge it to the size you would like and change the font until you find one that appeals to you. The number should be at least 4 inches tall to be visible from a distance, and the font should have crisp edges so the number is easy to recognize.
Print out the number onto a sheet of paper.
Place the paper on a cutting board and use a craft knife to cut out a stencil to use as a guide on your door. When you cut out the numbers, you can either use the remaining paper as a guide or use the numbers themselves. Using the leftover paper helps you maintain the spacing that the font designer thought was ideal.
Tape the paper or the numbers to your door in the location where you would like to paint them.
Trace the outlines of the numbers with a piece of chalk or a pencil, depending on what shows up better on your front door.
Open your can of paint and thin it, if needed, according to the instructions.
Apply paint with a thin-tipped paintbrush along the outline of the first number, working slowly and carefully to ensure that you have a smooth line around the edge. When the outline is complete, fill in the remainder of the number with paint. Try to use even strokes, so you have a smooth finish. Repeat the process with each of the other numbers.
Erase any stray chalk or pencil marks with an eraser or a damp cloth after the paint has completely dried.