I go to craft shows regularly and have sold at them on and off for over 20 years. Here's some things to keep in mind:
1. See if you can find out about the competition or if there are rules about the type of products sold by each vendor. If you sell jewelry and there are going to be 10 other jewelry vendors there, unless yours is totally different it will affect your sales.
2. Try to sell more than one thing. When I was just selling cards, anyone who didn't send cards was automatically not a customer. This meant a lot of people who may have thought I was talented would walk right past my booth because my product wasn't of use to them. And I had to sell a heck of a lot of cards to make back my booth fees. You know who brought this to my attention? MY FATHER! Who has probably purchased maybe 5 cards in his entire life and rarely goes to craft shows. Wise words.
3. Don't over make but go for variety. If you always sell out of widget A, making 500 of them instead of the usual 20 is not necessarily going to increase your sales. In fact, it may hurt them. People will think they are so easy to make, maybe your price is too high. Or you're spending all your time on that item, a person may want a bit of this or that but all you have is widget A. Setting out only 5 or so of an item at a time and replenishing may be a better bet.
4. Change what you make. I saw this lady who had racks and racks of embroidered holiday sweatshirts. Honestly, her booth was stale and the style went out years ago. I could buy her stuff at Walmart cheaper and just as well made.
5. Location, location, location! A show I went to last month had placed items geared toward children in one section near the games for kids. Good and bad. Those without young children didn't go near there, although many could have bought for grandchildren. One booth sold handmade clothes for American Girl dolls. The booth was packed (great for them!). But directly across was a great booth, awesome display of original dolls with different outfits to buy. Booth was dead. If that booth had been somewhere else I bet it would have gotten a lot of attention. Make friends with event organizers or inquire on where you're going to be and ask to change if possible.
6. Location, again. And display. This one show I go to has an aisle where you can view booths from opposite sides. Some booths open for both sides of customers, some close off and you can only see their stuff from one side. Well, not everyone makes it all around. And it's just friendlier having an open display.
7. Talk to other vendors. You will learn so much and make great contacts. I had one lady next to me who bought ALL my gift tags for her soap, just because she didn't have time to make her own. She even gave me some free samples of her items, just because we were chatting. The other people next to me sold candles. Creme Brulee (sp?) was their best seller. Who knew? They actually taught me a lot about inventory and production. They had it down to a science by just writing down what their customers purchased at every show over the years.
8. This one is going to be VERY controversial. I may get hate mail over it. I LOVE making paper crafts. But I don't like making things that are just going to be looked at, wrappers opened, and tossed. Do I really want to dress up a candy bar and triple or quadruple the price to make money? Does that show my talent or creativity? The craft needs to evolve. Make some of the pictures with different designs or larger framed pieces. Or banners or pennants that can be used over and over. You can do amazing things with paper! That adorable Santa you wrapped a candy bar up as could be in a frame or ornament instead and used year after year instead of tossed. You can increase your price for the item and it'll last a lot longer than the memory of eating the candy bar.
9. Stores aren't stupid. Something priced at 2 for $1 vs 50 cents each just sells more at 2 for $1. I price all my cards at $2 or 6 for $10. Sell lots at 6 for $10 all the time. People think they are getting a deal. No, my cards aren't the gorgeous pieces of art that I see in the magazines or on here. But they are still cute and adorable and when they are tossed I won't feel nearly as bad. In fact instead of making a cute, adorable, awesome, complicated card, put that piece of art in a frame! You'll make more money for the same amount of time. If you have an Ikea near you, their frames are wonderful.
10. Turn your craft into art. About 20 years ago my husband and I bought this neat paper cutting of a butterfly and roses. It was framed and cost either $20 or $25. It's hung in my homes in various areas for years. That same item could have been on a card, which would have been tossed. Instead they framed it and I've had it and enjoyed it for 20 years now.
I hope some of these tips are helpful!