My Sim currently lives in Willow Creek in the lot by the special tree. She puts her stand on the corner of her property, near the path all the NPCs take past the tree and her stand is always full of customers; Some NPCs stop by, but also the neighbors in the other houses in that dead-end area stop by every time she starts a sale. I haven't tested using the stand in a park yet, but that would be my second choice, or I was thinking maybe in San MyShuno during a festival if that's possible--anywhere there is a lot of foot traffic already coming by.
I've only done it with putting the cooked food in my inventory first, but supposedly you can also put the small appliances in your inventory and put them on the stand and cook there in front of customers. I haven't tested that yet, though.