BOOKS AND ARTICLES:
Writing Exceptional Missionary Newsletters by Sandy Weyeneth
Weyeneth provides an overview of the importance of missionary newsletters and offers tips for improving one's writing. She also gives practical information about mailing, emailing, and using social media and lists many helpful resources including other books to read and organizations that provide letter services.
All the News That's Fit to Tell and How to Tell It by Amy Young
Young focuses on instructing her readers how to improve one's writing and developing as a writer, giving practical instructions in the 'Your Turn' section at the end of each chapter. She gives a great overview of her book in a blog post on A Life Overseas.
For a brief overview with some tips, check out these articles:
Newsletter Ideas for Overseas Workers on Our Goodwin Journey
Ten Steps to Writing a Memorable Missionary Newsletter on TEAM website
How to Design a Beautiful Missionary Newsletter in 5 Steps on TEAM website