Make more roles but with smaller responsibility
Make a description for each role
Make a Year-Wheel with tasks throughout the year.
E.g. use the first year to note down each task, then the list is ready for the second year
The tasks should be clearly described and have clear deadlines if at all possible
What is the task?
What are the success criteria?
What is the time frame / deadline
The list of tasks and descriptions can be sent out prior to the players' meetings
Tasks should be devided to players during the meeting
More players' meetings will give more volunteers!