If you are selling any clothing, be sure to put the size on the tag. If they have to dig around looking for the size, they are likey to just pass on it.
Watch for shoplifters. We had that experience. Several people come in together and a couple create a disturbance while the others steal. Especially jeans. They know you are not experienced at watching for such goings on.
If you have electric things, have an extension cord out there so they can plug things in to see if they work well.
Have a sign that says "Not responsible for accidents" because there are those who come just to pull that one on you too.
Have an area with a few toys that children can play with while the parents shop so the kids aren't into everything
Millie