Plan for the unexpected.
They say success is opportunity meeting preperation. (Or something like that) I recently filmed a commercial. What impressed me was how prepared the crew was onset. They had the day planned to the minute. The were ready to move and grove but even with their high expectations, the crew also rolled with the unexpected surprises and worked them into the plan.
This is what separates at the hobbyist from the professional. Winging it will only get you so far. If you plan on being a pro, then plan.