taking a class is the quickest, but most expensive route (usually.)
It's like college. Realistically, you could learn on your own, but college (used to) expedite that by allowing you to have access to (in past years) subject matter experts.
Money I spent on a physical therapist/personal trainer was well worth it for me.
As a few people mentioned, a lot of it was weak core muscles / not "moving" or utilizing the proper muscles when moving.
Add on stress to these errors, and I had huge issues between my shoulder blades and other...