Be confident in your abilities. I took the practical five years after the theory and gained alot of experience. If you don't know something, or are unsure, say so and then find the answer out.
Make sure you tell your crew what you want them to do and don't ask them to do things beyond their level of competency. Remember, if it goes belly up, it's your fault and responsibility!
Make sure that everything is stowed promptly, tidily and in the right place - be on top of the job and aware of what's going on both in the boat
and in the wider area, don't be afraid to delegate and make sure you get information and feedback from the crew.