Some pastors meet all departments on a quarterly basis while others meet monthly. They also have tag-in sessions with department heads on a weekly basis. Basically it depends on whatever works best in your situation.
It may also depend on how large the church is, how many departments exist, and the scope of their responsibilities. Some departments need to meet more often than others.
Many churches have annual meetings to plan a basic outline for the year. They set aside enough time for each department to present their goals and vision. Of course, they also meet on a regular basis to make adjustments as needed.
It may also be a good idea to have a three month planning calendar. You can meet each month to finalize plans for the upcoming month and also make preliminary plans for the other months that can be finalized as they get closer.
Whatever the schedule, it is vital to carry through with it and not allow too much time to pass between meetings. Such meetings are important for accountability and continuity.