Re: Crown Molding
I prefer to cope inside corners unless the walls are solid paneling or cabinetry, where you can get away with miters, but copes are so much easier.
Your initial piece will have two butt ends, and the last one with have a cope at both ends. Cut it 1/16" longer so it springs into place.
Make a "test cope" from scrap, and hold it up in every corner along with a butt-end piece to see how your cope aligns. Mark in pencil on the walls and ceilings where the crown needs to rest to make the best joint. Follow these marks as you nail up the actual crown.
If you back-cut your copes a bit, you can readily fine-tune them with a little sanding. For "watertight" copes, glue sandpaper to a scrap of molding, and use that as the platen to get the most perfect copes for stain-grade work.
Remove not the ancient landmark, which your fathers have set.