Markets aren't always held inside where it's nice & warm and the weather has no effect on your stall. So when setting up a stall outside you have to be aware of wind! Wind was my first issue I came across, I wasn't prepared for it and didn't bring anything to hold my tablecloth down. Thinking back now I feel very naive in not allowing for this problem, so I tell you now bring clips or weights to hold down your tablecloth!
In case of rain it's good to invest in a really good marque/gazebo. If you think you may be attending a lot of markets and they are outside then I would highly recommend buying one, it's a great investment. I bought mine from boating, camping & fishing which you can see it online here. My gazebo is easy to put up by myself but I've found that other stall holders are more than happy to give you a hand if you ask. You may even need to buy some sides for your gazebo so it keeps out the rain and wind. You can buy tarps and lots of hand clamps or you could buy the proper sides for this gazebo which are so easy to put up as it's made perfectly for your specific gazebo. I purchased my sides from a local Bunnings Warehouse, just make you buy the correct ones!
Another tip for having a market stall outside is that you should always wear something comfortable and warm because you're at the mercy of mother nature. So if you're not warm and comfortable then you will be miserable all day!
Important things to take with you to a market are: a pair of scissors, sticky tape, pen, paper, bottle of water and some snacks.
I hope these tips have been helpful and I'd love to hear any tips you may have during your experiences being a stall holder