For particularly large sprites, it's probably not a bad idea to make 3D models first, then animate and paint over them. It's a lot of work but at least your characters will be anatomically correct, which can be difficult without reference.
As for the animation itself, I dunno..I've always found it to be pretty easy to figure out how something should move. If you really have to, make a "skeleton" or wireframe of the character animation first, then draw over it. It will be easier to tweak that way.
Another "trick" is to make your entire animation in a small amount of frames, and then add "tween frames" to smooth it out. I do that a lot, especially for walking animations.
Mike Judge once said "If you're going to be an animator, you should probably take physics classes"...or something like that..It's really not a bad idea. Learning physics can teach you how things should move and interact in the real world. Crappy example, but think of a rubber ball. It doesn't just hit the ground and bounce, it flattens out as it comes into contact with the ground, then turns into a sort of oval and moves upwards. Only when it's back in the air does it go back to its normal shape. It will probably jiggle a bit afterwards, too. A good animator will take this into account, and probably exaggerate the shaping of the ball, and maybe even add some dust particles or lines/dashes to show the ball is moving at high speeds.