If the question is about praising a manager's contributions, I would say that like all letters of support, there should be some basic elements present. It is extremely important to derive at least three specific supports or reasons as to why this manager has earned praise. I would ensure that each reason remain distinct from one another. Each reason should have sufficient detail to bring to the reader's attention why praise is worthy. Essentially, you understand the reasons for the praise. The reader, alas, does not. Hence, your task is to persuade the reader to your point of view as to why what is present is worthy of the highest of distinction. Certainly, part of this would involve a small introduction of how you were in contact with the manager and your capacity in writing this letter, noting the praise. Yet, you should develop these clear and focused supports which bring to the reader's light what you in your own mind have already concluded about this particular manager.