From 
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1. Experiment with built-up molding combinations to make your decision easier. Nail or glue samples together and hold them against the ceiling.
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2. Run masking tape around the walls and ceiling so that about 1/2 in. of the tape will be covered by the rail trim. Mark the rail positions with a chalk line. Locate studs and ceiling joists.
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3. Find the right miter angle for the ceiling rails at inside and outside corners. Miter scraps to 45 degrees and hold them in place along the chalk lines. If there’s a gap, adjust your saw’s angle and cut again until they fit tight.
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4. Glue the ceiling rails into place with construction adhesive. Nail the rails to joists wherever possible. Where you can’t hit ceiling joists, drive nails into the drywall at a 45-degree angle. Angled nails will hold the rails in place until the adhesive sets.
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5. Nail the wall rails to studs with 2-in. brads. Cut coped ends for inside corners. Then miter outside corners using the same angle-finding technique shown in Photo 3.
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5. (cont.)
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6. Measure the run and drop of the crown molding. Then nail two blocks together to make a marking gauge that duplicates the run and drop.
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6. (cont.)
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7. Mark the position of the crown molding’s edges on the rails using your gauge. Place guidelines at all corners and every 2 ft. along walls. Use the marks to position the crown.
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8. Measure accurately using a two-step technique. First measure from a corner and make a mark. Then measure from the other corner to the mark and add the two measurements.
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9.Square-cut both ends of the first piece of crown and nail it into place. All the other pieces are cut square (or mitered) at one end and coped at the other.
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10. Attach extensions to your miter saw’s fence with screws or hot glue. Then screw on stop blocks, using your marking gauge upside down to position them.
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11. Cut crown molding at a 45-degree angle to prepare for coping. Place the molding upside down against the stop blocks. Before you cut, make sure the direction of the miter matches the slash mark.
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12. Cut a cope by following the edge left by the miter cut. Hold the saw at an angle to undercut behind the face of the molding. With many moldings, you have to cut away one section to get at another.
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13. Test-fit the coped end using a scrap. Perfect the cut with a rasp. If you need to remove lots of wood from the backside of the molding, use a sanding drum and drill.
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14. Push the coped end into place and check the fit. If the cope fits tightly but the piece is too long, shave the square-cut end on the miter saw.
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15. “Spring” sections of crown into place. Jam the square-cut end into its corner. Then bend the middle outward as you guide the coped end into place. Let the crown straighten to force the coped joint tightly together.
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16. Mark the length of outside corner pieces by coping one end and holding the piece in place. To get the angle right, use scraps of crown and the method shown in Photo 3. Draw a slash mark on the crown to indicate the direction of the miter cut.
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17. Miter outside corners with the molding upside down. Cut the piece about 1/16 in. beyond the length mark and then shave off a bit if the piece is too long.
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18. Check the length at outside corners using a test scrap. When the length is right on, set the piece aside. Then cope, miter and test-fit the other outside corner piece.
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19. Erase small cracks in outside corner joints by rubbing with a utility knife handle. This crushes the wood fibers inward and closes minor gaps.
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20. Join sections of crown on long walls using “scarf“ joints. Set your miter saw to 22-1/2 degrees and make scarf cuts with the molding upside down just as you did for other miter cuts.
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21. Remove the masking tape after finishing the crown. Run a sharp utility knife lightly along the rail to slice the tape.
Copyright ©2005 Home Service Publications, Inc
Woah! This is AWESOME! Especially for a visual / kinesthetic learner like me. I feel like I can tackle my first job at my parents house! Thanks!