We all know the trouble you could encounter if you wait until the last minute. Sloppy work is one of many issues. Most crafts and pieces take time and focus. If you are watching the clock the night before speeding around and finishing everything, this is not a good sign. Take time with your work and stay calm. Get a good night sleep the night before the convention and have a big breakfast early in the morning. It is very important to have a good breakfast before a long days work. (most times you will be work 12 hours and you won't be able to get lunch!!)
Practice your display.
At Animazement I sat next to Ryan from MoogleGurl, her display was tall and well planed. She had a banner with her shop name and all of her items were on a vertical display. However, I had no idea what my display would look like until I was setting up. Your display will be what draws customers in. A display should show off all of the products and help a customer see everything you have to offer. When people are walking around a convention they might not have a lot of time to stop and look at everything so your display has to be clean and organised so people can clearly see your items. It's a good idea to set up a practice display at home a few weeks before the event to get a feel for the display.
Keep logs, make goals, and have a plan.
Next, it helps to keep receipt books to keep tract of the items you sell and to help you figure out what to make the next year. Try to make small goals to help you stay focused and stress free. For an example, "I will make 50 cupcake but the end of this week," this is not a good idea because it make you feel like you have to make 50 cupcakes now which can throw you off if you are working on other projects. Instead plan on making 10 cupcakes a day alongside with the other crafts. Lastly, plan on what to make and try to figure out what would sell best. This could take some research but it really helps. You can look around your gallery at what has more comment and favorites, you can also look around for themes and get inspired from other artists around the net to get an idea of what hot and selling now.
Try to not get overwhelmed and stressed over the upcoming event. It takes a lot of work to run a booth but it's better to not think about how you have to do or what little time you have left to work. You can get more items made if you take your time and just focus.