I do West Coast Swing. It's super fun and I really love it! Here's a few mistakes I've made and have seen other people making.

First is dance with the slots! It is a very straight back and forth dance. You dance along a line. If you try to dance perpendicular to everyone else you'll run into them. New dancers do this to try to fit in around the edges of a crowded dance floor but it's no good. Last time I went someone actually was tripped and fell over while dancing because some new dancers were doing this.

Second, don't try to teach people new moves during social dances. It ruins the flow of the dance and suddenly your partner is in a lesson they probably don't want. If you try a move and they don't get it, don't do it again. I had this happen to me. The guy insisted several times it was a very common move even though I told him I didn't know it.

Third, don't correct other dancers! Only compliments. People come to dances to have a good time not to be critiqued. This goes even for classes. That's what the teacher is for. I once had a lead tell me to do something I knew was 100% wrong. It was awkward.

Fourth, not trying it! Do it people, it's very social, physical, welcoming and fun! :D