I have been doing them for ...a long time. Biggest tip ... pick your show carefully. Small shows = small sales. Look for well established shows( means people go to buy, or they would not still be around). I wasted too much time doing small shows , remember its the same amount of time sitting at a small show as a larger one. Do not be afraid to enter juried shows, this means that amougst the sellers there is competition to get in , thats a good thing, means people are selling. It also keeps the quality higher than non-juried shows.
People buy more items priced from $5- $50 than higher priced goods. Remember when the customer went to the show they had no idea of what they would see/buy. So most items are impluse purchases.
Fall shows are typically higher for sales ...people looking for gifts.
Research a show buy attending , what is selling what is being packed up at the end of the day.
Most of the better shows require photos of your work , make them high quality photos that really show your best work . They will be making a decision based on what is in those few photos. It is not unusual to have to apply many months prior to a show . Most of the fall shows are putting out the applications now. Go on line for the shows in your area and see when applications are due. Read ALL of the applications requirements. It would be a shame to be turned down because you missed something in the application. Oh most of the bigger shows do have an application fee.
It takes a while to find your niche... but it can be done!
Just one word of caution ... taking a much loved hobby and turning it into a business , can result in the hobby not being loved/fun quite so much.