Regular meetings. Meet with the preceptor before the course begins to establish expectations. Also establish regular meetings (weekly) to facilitate communication about potential problems or particular ideas they may have.
Clear expectations. Be explicit about what you want the preceptor's role to be. Should they be involved in the classroom? What will be their role in commenting on papers? Do you want them to suggest ideas for assignments? Should they hold office hours (how many? how often?).
Have your preceptor's back. State clearly to the class what the role of the preceptor is, including the importance of the class in respecting the preceptor's time and private space. Keep the preceptors in the loop about developments in the classroom.
Encourage new ideas. Preceptors are filled with ideas. Encourage them.
Engage the preceptor. There are a lot of ways in which preceptors can be active in the classroom. Encourage preceptors to play an active role, including possibly leading a class or discussion sessions.
Be aware of other commitments of the preceptor. Keep open communication to help plan when heavier workloads may be needed.