As a motion designer, you probably know a lot about After Effects and Cinema 4D but might have little to no clue about Adobe Illustrator. However, Illustrator can be very useful ( maybe even more than Photoshop) for your motion design work as you’re able to import all AI files in After Effects and Cinema 4D while keeping all the splines information and whatnot. This tutorial by MographCandy will learn you everything a motion graphics designer need to know about Illustrator:

Adobe Illustrator For Motion Graphics Artists: An Introduction from Mograph Candy on Vimeo.