This is a good one:

14: Try to work in a restaurant close to what your operation may be like, learn how to cook on a grill, work on a fryer, or just work a restaurant food window learning good customer service. Like I said earlier, you are a professional Restaurant on wheels, just as important as anyone else in town, look and act professional, and you will be respected for doing so.

Working with customers will help you grow some skin!  You don’t want to be a newbie around professional hot dog eaters or when the local cronic complainer comes along.  You need to be alive, talkative, have some trivia and so on. 
I know from my own visits to carts, there is nothing worse than walking up to a zombie vendor that has absolutely no communication skills!