Examine your walls to ensure they are clean, smooth and free of damage. Remove any dust or spider's webs. Fill and sand any holes prior to completing the next steps.
Determine the desired size for your molding. For rooms with average ceiling heights, 4-inch molding is appropriate. If your walls are shorter or appreciably taller, you may want to choose thinner or thicker molding.
Use your measuring tape to measure 4 inches from the ceiling down the wall. Mark this height with your pencil.
Continue around your room marking at 4 inches approximately every 2 or 3 feet, depending on the length of your straight-edged ruler or lumber. Be sure your straight edge can easily reach between two marks as this will make your next step much easier.
Lay your straight-edged ruler or lumber along the wall along your marks. Draw a line connecting your marks using your straight edge as a guide.
Lay your painter's tape along the line you marked. Make certain to align the top of your tape with the pencil line so you have the full 4 inches of wall above the tape. Press the tape firmly ensuring it fits tightly with the wall to create a clean, crisp paint line once painted.
Seal along the painter's tape to help keep your molding paint color from bleeding under the tape, if your walls are especially textured. To do this, simply apply a thin coat of glaze or the original wall color along the tape line, overlapping it so you have about 1/2-inch of paint on the tape and 1/2-inch on the wall. Let this dry before proceeding to the next steps.
Paint the 4-inch space above the tape with your chosen crown molding color. Along the ceiling line carefully cut in your paint while taking care not to get paint on the ceiling. If you have difficulty with this, you may want to use a piece of paper or a manila folder to protect the ceiling while you paint up against it.
Allow your paint to dry. Once dried, remove the painter's tape to reveal your new, faux crown molding.