1. Pack a small bag with items which might just save your day - eg blu tac, scissors, drawing pins, a pen, pencil, rubber - you never know exactly what your space will be like and these small items have always come in useful to me in the past.
2. Make friends with stall holders round about you. They can be a great help watching your stall while you nip to the toilet or grab a bite to eat. Fellow stall holders often offer each other discounts or freebies which is a great way to network too!
3. Have everything clearly priced. Customers often believe that if they have to ask the price it must be expensive.
4. Make sure the event has been well publicised. Ask the people running the event if they have created a Facebook event and invite your friends, offer to put up posters or hand out flyers.
5. Take a cloth to cover your table and use boxes or crates to create different heights to your display. This will add interest and make your stall more interesting. If it's Christmas time perhaps add fairy lights or battery operated tea lights to give it a festive look.
I hope these small tips help you if you are setting up a craft stall, please let me know if they do!