1: Avoid too many words when writing a newsletter. Make your news letter as concise as possible. The average reader has a short attention span.
2: Avoid typographic errors. Ensure it's proof read by someone with proof reading skills and an eye for detail to spot such errors.
3: Avoid grammatical errors. Before publishing, ensure it's read by someone who boasts good editing skills and experience. Readers won't take you serious if your newsletter is filled with grammatical errors.
4: Ensure you have a creative subject line capable of drawing attention and interest. Many subscribers are wont to dismiss a newsletter with a banal subject line.
5: Quit trying to sell your organization, products and services to readers. Instead give useful information and valuable content that would keep readers hooked. That way trust is built with readers and they are bound to contact you when the need arises.