You must also be decided on, if you will allow your shown work to be lain away, and the terms in doing so.
I have sold art, paintings, drawings, ceramics and woodcuts (hand printed inked prints) on time in the past but few people will actually broach that topic, on their own; they seem to be afraid of upsetting the artist/photographer, so you must offer that option option during your conversation.
By-the-way, many galleries will also sell on time, so ask when your looking to buy art.
30 to 60 days is typical but if they're cute, 90 days is also a choice.
Pick an upfront, deposit percent, I suggest a third or half percent, non-refundable fee, so they understand they'll pay a 'penalty' for no following through and so you know that they are really interested in getting your piece and you'll receive a compasation for your time and the loss of possible sale of the piece, while it's in your storage or studio.
Keep a generic receipt book, whole, with two copies and the original, which you keep, with their signature, and you give them the pink copy, with the yellow staying in the book, always.
A ink stamp with your business info speeds things along and a simple filling system of twelve (12) long envelops, one for each month of that year, will serve well enough for all purposes.
Detach from book and file white receipts only once, when last payment is made, with their signature for final pickup and note any commission or fee you pay for the space you're renting/selling from.
Seek legal advice on your State and Federal obligations, including taxes.
Advertise photographic prints and the hours when you'll be on site and ability to discuss your art and methods, etc.
Be there during those hours and add patrons contact and info to your notebook.
Good luck with your show.