Snap a level chalk line and mark studs before fastening it to the wall. At the corners where walls meet ceilings. Heirloom and dentil are most common for crown molding. Like crown, bed molding is all the same basic shape but with a concave rather than convex top third that varies in width. For cove, the convex curve is either tight or wide.
Wider cove is more graceful.
Bed molding averages 70 cents per foot, with wide pieces priced higher. Installing wood crown, bed and cove molding is an advanced project, so you may want to get some outside help. Outside corners require compound miter cuts, while inside corners must be precisely coped. Depends on width and grade. Installing baseboard is easy, even for first-timers.