Let’s say that I have a feeling there should be five steps in this scene, including the first pose. I go to my 3D graph editor, or to my Flash timeline, and I put three more keys on it:

An uneven number of steps of course makes my life easier at this point, because I have a middle key to help me get oriented. How lucky that my well-trained professional eye has determined that five is the exact number of steps I need to make.
Now I change the tangents to “stepped” in 3D, or turn off the “motion tween” in Flash:

The result:

As I watch this, I have to keep in mind that every other step will be on the right leg. I’ll do that soon enough. The important thing now is to determine the rhythm of the walk. I will switch back to the “linear” or “classic tween” version and add or remove steps until it looks right.