This book explains it all in a very easy-to-understand manner .. .. ..
I've used it for reference many times over thae past 4-5 years .. .. ..

http://www.compoundmiter.com/molding.html



While it is possible to match the pattern when making a scarf or butt
joint, it is not possible in the corners. What is the best way to
handle the inside and outside corners? Just make the cut and match the
best you can? Use some caulk to feather in the mismatched contours?
Show guests your new crown molding with the lights dimmed?

Q2: We have bull-nosed outside corners. This means there will be a
small gap at the bottom where the molding meets in these corners.
Would it be best to cut small quarter round plugs out of 1" thick wood
that would slip up into these gaps? Or does it work just as well to
fill the gap with a little caulk, smooth it out, and let it go at
that?