If Christina or Kate were still readin' CD, they'd be a great help to you, since they're the resident ballroom dancin' folks.
Clothes that are easy to move in are best, obviously, and if you're going to wear a skirt, make sure it's 'flowy' and not constricting. Wear comfortable shoes
Dancing beats up your feet. Avoid sneakers, though, 'cause the rubber soles and the dance floor aren't exactly the best of friends. It'll just make moving harder.
That's my advice as a frequent bystander, and much more infrequently actual dancer. Maybe if life works itself out, I'll take Beginner Social Dance one semester. . . maybe not
Ballroom dancing folks are cool, generally, so, score one point each for you two