I am not a trim carpenter, and I don't install crown molding very often, so I always need to practice a bit before I am comfortable cutting expensive stain-grade materials. (Measure twice, cut once, really applies to crown!)
The patented EasyCoper really simplifies the task of coping crown molding. It consists of right hand and left hand guide plates that are screwed to a work surface, slightly overhanging the edge. (I'd attach them as a pair to a board that I could then clamp to a pair of sawhorses.) After mitering the end of the molding, place the crown in the guide, face up. Then use your sabre saw like a coping saw to remove the waste material by following the molding profile exposed by the miter cut. The large flat end surface is beveled so that you can follow the profile at the perfect relief angle, and there's plenty of visibility, so it's easy to do. EasyCoper is designed to cope crown moldings with a 52/38 degree spring angle (the most common), but includes instructions for use with 45 degree crown as well, and it works with crown up to 5-1/2" wide. The Festool 486564 blades will work with this product. Made in the USA with durable plastic.