When on set, or on site for any production the worst thing you can be is unprepared. In this line of work clients are looking for a certain level of professionalism, and being prepared is apart of that. Some actions you can take to insure that you are ready for your tasks are:
Have a checklist to ensure you know what you have and what you need
Have someone check the list behind you, to have another set of eyes checking behind you
bring two of everything because things do happen and things do go out
be on site ahead of time to set up and make sure everything is in working order
