I do not specifically work on any "footwork drills", persay. I do, however, pay very close attention to the footwork that I do, and correct it when I see that I am putting myself into an unstable position.
One of the things that I have recently spent a lot of time paying attention to is my center of gravity. I have discovered that in clinch situations, I was remaining too high, and needed to get lower. I believe one of the reasons underlying that tendency was that I just did not spend enough time lower, and so was uncomfortable there. The other contributing factor was that I wasn't strong enough on my base when it was lowered, and was therefore not quite as mobile. Mobility, for me, is key to survival. I'm not a large bulky man, and need to be able to move and position in order to find success. I decided to work the problem, and see if I could generate any results.
What I've done is basically gotten down very low, in a right lead, and felt my center of gravity. I then slowly shift my center from one foot to the other, gradually speeding up the shifting, all the while conscious of my center, not letting it go. I get to the point where I feel as though I am "tossing" my center back and forth, from foot to foot, and simply carry on with this until I get bored, and then switch it up. I remain low in my stance, but begin to "shuffle" my feet around, whilst maintaining that "tossing" feeling, so that my center is always under control. This may not have translated very well into words, but, wotthehell.
That's my footwork story.