Remember, there is always more work to be done than time to accomplish it. After you've established the To Do list, flag the tasks as Vital, Urgent, Time-Sensitive, of Limited Importance, and None of the Above. Vital tasks do not necessarily have to be done that day but must be accomplished prior to the deadline. Urgent matters require prompt attention but may not be important. Be realistic in assessing the time required for any task.
Priorities are meaningless if the time allocated is unrealistic.
Above all, set reasonable expectations. Establish deadlines for each task, and calendar them. Include regular daily activities in the To Do list. Leave time for unexpected matters. The office is a team.