I don’t operate out of a food truck, but have a tent set up. My responses are limited to outdoor festivals and not day-day setups in parking lots or city streets.

I’d say one thing many food truck owners don’t think about before getting into large outdoor festivals is typically you are paying for a 10x10 space, so trucks are usually bigger and need to pay for 2 spots, which can be pricey and hurt your net profit. Other general thoughts:

1. Knowing how much inventory to stock given food trucks usually have perishable items that cannot be carried over too long, so eventually become waste.
2. Permits and code for different areas. For example, one area we do many festivals changed their requirements for food trucks/trailers to have ANSUL systems, which can be very expensive. That change caused many people to stop operating in that city.
3. Know what sells at events. I’ve seen people try to introduce novelty food items thinking that alone would drive sales. In my opinion, things as simple as fries are some of the best sellers at outdoor events.