Like KN said, flare just enough so that the bullet will start into the case. Best way I've found to do this is to flare a little, then take the case out and try to start a bullet in it by hand. If it looks like it won't quite start in, you need more flare. Once you find the right spot, lock the die in place and flare everything with that setting. It's a bit of trial and error, kind of like finding the right setting on your powder measure for the first time.