One thing about motion design that often gets overlooked is the importance of being a skilled designer. Knowing the principles of what makes good design, understanding color theory, and becoming familiar with typography are all really critical for being able to create visually compelling animations. Personally, becoming better with the design principles and color theory is probably my biggest struggle as a motion designer, and one that I'm striving every day to improve on. To that end, I've found Skillshare to be a very valuable source for design courses in which industry pros teach everything from the four graphic design principles (C.R.A.P.) to specific techniques. I highly recommend checking it out!
P.S. There's also some great motion design courses on Skillshare from Jake Bartlett as well!