Well, in the Yoshinkan we use the practice of kamae and the kihon dosa. (6 movements) It can be done either alone, with a partner or with bokken. The idea of this movement is the help make the body strong and balanced, yet be smooth and relaxed. That's the corporate answer.
A drill that I was taught at an Aikikai school was called leading the blind. What you would do was to have one person close their eyes and the other would guide them around the mat, moving uke in various directions including circles. We would finish by lightly, at first, throwing uke with a front or side throw. The idea here is to see if you, uke, can sense the movement and flow with it.
When you are really stiff, you cannot stay connected and you end up walking hard, versus sliding your feet. When your are relaxed, breathing and relaxing the shoulders, you get a better feel for this.
In our basic kamae, we really focus on keeping the shoulders down. Relaxing them to where they feel like they are sinking toward your center and projecting forward. Of course, coming up behind your student and giving them a shoulder rub and saying
"RELAX" and "BREATH" helps too.
Come to think of it, I've been giving an awful lot of shoulder rubs lately ... hmmmm ... Might have to rethink that.
Don't know if that helps or even makes any sense. Breath and relax the shoulders. And practice practice practice unitl it becomes a natural movmement. That's what I focus on anyway.