Must haves for me:
Really, really great lighting so the fabric colors are easy to see and match up. Perhaps even a couple of Ott type lights at work tables.
A coffee pot on at all times!
A small table for hubbies/others - put out a jigsaw puzzle and a few Sudoku books.
A place to set out fabrics and match them up.
ALL, and I mean ALL, employees must treat each customer as though they are important. One quilt shop I go to has a super friendly owner, but if she is not in the shop, the gal or two that work there act like the women they know well are wonderful, and every one else who enters the shop are aliens who must be held at arm's length. They chat and go about their business and act like you are bothering them if you ask a question or want to get fabric cut for Pete's sake...
A clean bathroom!
Posted shop hours that are adhered to.
Good luck with the shop!