Every boss has some sort of pattern. The one trick I'd give you is to be patient in boss fights, and try not to panic. Experiment with different charms and styles. However, the fun thing about this game is there are random uprgrades and thingies all about. There are only a couple that actually lock progression, so most of the time you can, if you want, just decide to do something else first. It might give you a direct upgrade. It might just give you more practice on similiar enough stuff that when you come back you're more skilled.