Finding a mentor has been an invaluable experience. It’s so important to get a professional opinion on your work and just feedback in general, as this will help to give you an idea of your strengths and weaknesses. I signed up for a (free!) e-mentorship programme, called Prospela, and would recommend giving it a try, since the professionals on there are specifically dedicated to supporting you. I was matched with a storyboard artist and their feedback greatly helped to improve my portfolio, while their encouragement gave me hope to keep pursuing this industry.
You could try contacting professionals through e-mail or social media, but make sure the questions you ask are specific and thoughtful, as they can be busy people and sometimes you might not get a response at all. Avoid asking vague things like “how can I get hired in the industry?” or “what should I put in my portfolio?” as most of these answers can be found in a Google search. There’s lots of professionals that make YouTube videos about it too, such as Ethan Becker, Anoosha Syed or Michelle Lam. For some encouragement, check out Adam Duff’s videos!
If you take an animation course in university, the book, The Animator’s Survival Kit by Richard Williams, gets recommended a lot – and with good reason! It’s the best place to start with learning animation, since it breaks down movement into clear, easy-to-understand chunks, with lots of examples that you can try to emulate and study. This covers the twelve animation principles in great detail too.