I had the walkthrough for my first jewelry show two weeks ago. The email said to dress professionally, and honestly this dress is the most professional thing I actually own, so that's what I wore.
dress and cardigan: thrifted, boots: Urban Outfitters, necklace: made by me
Aside from accidentally getting off the bus at Broadway and Pine Street instead of Broadway and Pine Street E (or vice versa, I don't remember) and having to walk about 30 blocks further than necessary, the walkthrough went great. It really helped me stop worrying about the show because now I know just what to expect.