The Accreditation Association for Ambulatory Health Care published in their most recent newsletter the key principles for effective written communication.
The six principles include:
1. Knowing your audience's age, gender and reading level to develop effective written communications.
2. Writing concisely with as few words as possible.
3. Let patients know what they're expected to do, and what they can expect from you.
4. Limit communications to one topic per communication, and make your point twice.
5. Communicate the benefits for patients and make it easy to comply with instructions.
6. Use both verbal and non-verbal communication and present yourself intentionally with both tone and appearance.