I found these tips on the Internet that someone put together nicely. (Sorry, I don't have the exact source). I hope that you find them as helpful as I do...
1. Set up the subject head of your newsletter carefully. Clearly have your topic in the subject, so it stands out as being a topic the user is interested in. Have an issue number or volume number, so that they see this is a repeating message that they're watching for.
2. Keep a consistent schedule. Users begin to expect the message to come in on a certain day, at a certain time. That makes them less likely to delete it when it does arrive.
3. Write articles that provide your readers with a list of tips. Depending on the topics your newsletter covers, your tips could be on customer service or autoresponders, or you could provide your subscribers with a list of tips that help them to increase their sales or market their businesses more successfully.
You could also provide your readers with a list of your top tips on a specific subject such as "Top 7 Ways to Promote Your Website" or "Top Ten Ways to Promote Your Newsletter."
4. Write "how to" articles. This type of article shows your reader step by step how to reach an objective, such as how to write effective ad copy, get repeat traffic, or write effective meta tags.
5. Publish interviews. Contact experts on the topic your newsletter covers and request interviews. Most people will agree as it provides them with promotion of their businesses at no cost. Publish your interviews in article format or use the popular Q&A formula.
6. Write articles that focus on a current hot topic, trend or "seasonal" topic, such as how to increase sales during the holidays.
7. Provide polls for your subscribers to participate in. Publishing polls will help you to increase the number of people who read your newsletter because your subscribers will be interested in seeing the results. Your polls can also be used to help you decide on changes in your content, publishing schedule, or new things to add to your newsletter.
8. Provide your subscribers with resources related to your newsletter's topicsuch as places to promote their businesses, newsletters, etc. You could add these in a recommended resources section. You could also provide a list of your favorite resources such as your top 5 books/ebooks on newsletter publishing, marketing or web design with a brief description of each of your resources.
9. Publish an editor's note at the beginning of each issue. Use your editor's note to increase your profit by announcing any new sales or discounts you have on your products or services. Also use your editor's note to increase your credibility by providing tips on the topic your newsletter covers and by telling your subscribers how you've helped your clients or customers.
10. Provide endorsements within your newsletter for your products from respected experts in your field or list testimonials from your satisfied customers.
11. Add an "Ask The Editor" section. Write out thorough, detailed answers to your subscribers' questions within this section. This will increase your status as an expert in your field, which will lead to more sales of your products.
Use questions you get from your subscribers as ideas for articles that your subscribers will enjoy and that will keep them reading your newsletter.
12. At the end of each issue, tell your readers what your next issue is going to be about such as the title and description of your feature article or anything new that you have planned. This will help you to increase your readership by getting your subscribers to look forward to your next issue.