Flash Frame-By-Frame Animation: Keyframe and In-Between Basics

You can fill in the remaining frames one at a time using the same technique to find the appropriate midpoints and then draw with those guidelines; with onion-skinning turned on you can actually see your entire path of motion, and use that to adjust accordingly. I've squashed mine a bit more in some areas, and adjusted the actual position of each stage of the circle's motion so that instead of zig-zagging along straight paths, it follows bouncing arcs.