If you’re interested in this topic I really recommend The Animator’s Survival Kit by Richard Williams (the director of animation in Who Framed Roger Rabbit):
Survival Kit is an advanced book that dives into the deep end, The Illusion Of Life by Frank Thomas and Ollie Johnson [1] (two of the guys on a bunch of the early Disney features) and Cartoon Animation by Preston Blair [2] (countless MGM shorts) will give you a solid grounding in the basics.
The whole article focuses on expanding a list of principles of animation from Illusion.
Drawing on the Right Side of the Brain, by Betty Edwards. Learning to draw is actually mostly about learning to see; not seeing the objects as we usually do, but seeing the light and shadow that form them.
I second Animator's Survival Kit by Richard Williams, it's great. And Keith Lango's video course for 3D animation. These two are absolute best for learning intermediate/advanced animation.
Also, of course, Animation Mentor and 11secondclub competition.
Another valuable resource touching on the same topic: https://johnkcurriculum.blogspot.com/ The overarching theme is getting the most out of the medium and avoiding blandness and boring results.
I worked under him while this was going on. Learnt a ton from him. He's very good at teaching the fundamentals of drawing for animation; I would not be the pro I am without his cruel tutelage.
When all the details came out of what he'd been doing to Robyn, Katie, and a long string of other women, all my art skills felt tainted and nasty.
I'd prefer to attach warnings to all mentions of his stuff, to help anyone looking to learn about drawing know what they are getting into.
Way to mess it up from the get go. #1 as Appeal is not even close. You don't do appeal as an animator, you are not a character designer. You give life to someone else's creations. The same goes for #2. Not a bad updated list otherwise.
There may be separate character designers in big productions, but that's not what this is aimed at. An individual learning to animate for their own purposes will almost certainly be both character designer and animator.
Also, from the article: "The sequence is not ordered by priority."
https://www.amazon.com/Animators-Survival-Kit-Richard-Willia...
Most of the points from the article seem to be derived from the stuff the book covers in more details.