I'm watching the Rebels animated series first, as Ahsoka seems to be a sequel-of-sorts to it.
I know it's not mandatory to understanding Ahsoka. but from the first episode, Ahsoka felt like a continuation of something - much more so than the previous live-action Star Wars series. So I figured I needed to acquaint myself with these characters before diving in. I'm halfway through the second season of Rebels.
HBJ