Draw out your origin and destinations in frames 1 and 4(or 3, but I'll get to that later). These should be rather different than each other, of course. If your character's fighting stance is bending his knees with his fist to his chest, you would generally draw out his most extended and most retracted in the two frames. An attack is far more direct, just drawing the start of the attack and the end of it. From here you would use 2 and 3 as tweening frames.
But what if the stance isn't so linear or you want to have a frame dedicated to going back to the stance from an attack? It's fairly simple, just move your destination to frame 3, and instead use 4 as a tweening frame.
An important thing to remember is that your character (most likely) has limbs with joints at least somewhat similar to your own. They should bend at consistent points. While sometimes you can take shortcuts in animation and get a decent result, doing things like just moving the foot then cutting meat off the thigh and ankle to make it fit again typically are very unappealing.