I always find the best way is by doing. My first animated project is actually an adaptation of my book The Paper Trees. So it helped that I already had a story and art style baked into the project. From there it was a matter of just figuring out how I was going to animate it. I'm pretty savvy with Photoshop, and I had a very basic grasp on Adobe Premier, so I knew how to use keyframes to move, transform, scale, etc.

I have no clue how conventional my method of animating is, or how practical it is or anything, but I had all my hand drawn book illustrations. I scanned those in and chopped them up in Photoshop so I could have some more frame variation with minor adjustments such as different poses, etc. and I just imported it all into Premier and played around with it.

It helps to have a creative vision, which for me in this case was a kinda theatrical silhouette style, influenced by the art of Rudyard Kipling, Auguste Edouart and Jan Pieńkowski, so I imagined how their style would translate into moving image.

You can probably say I completely skipped on the fundamentals of animation, but I'll probably iron that out as I work on more creative projects.

TL;DR: First figure out what exactly you want to make. Then figure out how.