Nothing. Animation by its very nature is a tedious, slow process. People who are already good at it can still take months to do something like pic related.
But getting good in general? Assuming you know how to draw (Which is mandatory to do animation; without it, it'd be like learning how to form sentences without knowing the alphabet), I'm just gonna copy-paste my answer for when I get this question (I'm some random SVA graduate):
You don't have to go to go to school, there are many resources to help you learn. Richard Williams Animator's Survival Kit being the most popular one, as well as others like Preston Blair's Animation Book, Eric Goldberg's Crash Course. And some online resources:http://monstroanimation.blogspot.com/p/animation-article-database.htmlhttp://tvpaintanimation.tumblr.com/post/11543257728/rough-poseshttp://animationbits.tumblr.com/http://framexframe.tumblr.com/
It also helps to watch other animators work to see their process. A good video to start with is Glen Keane's demonstration at CalArts:https://www.youtube.com/watch?v=cHbA6lG79Eo
The last and hardest part is finding other good artists you trust to give you constant critique, since it's very hard to improve solely by eyeballing your own work. You may not know what's wrong with it to begin with so you won't know what mistakes to look for. If you really struggle to find someone talented enough that you trust, you could always shell out a few hundred dollars on online courses where your teachers are professional animators who currently work in the industry. They'd give you both assignments and critique on anything you asked and while it would still be expensive, it's ten thousand times cheaper than four years of art school.