I've been told to keep my ankles together, and not "twist up my legs" because I "have a retarded left foot" *snicker*.

It's not "just" the ankles or feet or even up to the knees- it's the whole of the body. I think of it as "closing" each time I swivel, that way my whole body's aligned and my lead-arse doesn't sag behind. Well, it still does, but at least I can think about it *while* I'm getting bellowed at.