New to Dressage - Things to know? Books to read?

I’m just starting Dressage and have FINALLY found an awesome instructor.

Just wondering if you experienced Dressage masters have any tips for me? Or perhaps book/ video recommendations (especially if you know any good YouTube channels!) ?

I’ve been reading Jane Savoie’s Dressage 101 and watching her videos. Good stuff! As far as i can tell… XD

Also! I’m hoping to compete at some low level shows this summer. What organizations/ registries might I use to find and register for those? I’m in Denver Colorado if that matters.