Girls, this is the fun part. If you're going to be taken seriously as a swing dancer, the dress you wear must have a full skirt. If you don't do any aerials, ok, you can be flexible with the skirt but it just doesn't look as good. Skirts should come to the knee or a little past. Fabrics that breathe the most are wool and cotton.
Rayon is ok too.
There's nothing that looks cuter than a little sweater to match your dress. Especially in the winter months, where a coat over your dress just won't cut it. If you're going to wear pants, though, do it right. Dress pants with suspenders are de rigueur , as well as nice-looking dress shirts or blouses. When the weather's nice, capri or cigarette pants with a sleeveless or short-sleeved blouse is also a great look.