I have the same goal as you, friend. The answer to OUR question is: EVERYTHING!
As an animator, you should be able to draw EVERYTHING. Main things to study are anatomy (of humans, animals, monsters, as well as objects, such as cars, houses, nature, etc.) and perspective. Of course you should also be familiar with tone in order to convey depth. But I'd say that anatomy and perspective are the main ones to really grind.
1 minute, 30 seconds? These are just warm up sketches to loosen up the arm and the mind. I'd say do the whole thing. Do the quick ones, as well as the looong ones. Also, DRAW FROM LIFE. This one is really important. I know that animation is your goal, but if you know how the real world moves, your animation becomes much better.
Hope this helps. Remember to enjoy the process of learning... because this is gonna take a while...
I'd wish you good luck, but that's NOT what we need to succeed. What we need is to SHOW UP, WORK OUR ASSES OFF and SACRIFICE petty distractions.
