Writing a newsletter is an art by itself!  That's because newsletters tend to carry a lot of information in a friendly note to the audience.  Therefore your primary focus should be on your audience.  Keep your audience in your mind while designing a newsletter.  

There should be an aura of storytelling about your newsletter.  Its content should be simple and it should convey about your business intent in a soft manner without being characterized by too much of sales pitch.  Newsletters should be readable and should quickly deliver the information your audience is looking for in a highly professional manner.

You must give utmost importance to the parts of newsletter like subject line, header and include CTAs nicely into your content, thereby compelling your reader to go to your business page much to your satisfaction.  Use of bullet points, video and graphics is recommended.  

At the end of the newsletter you would do well to include unsubscribe link so your newsletter does not look spammy.  Include one or two testimonials and case studies related to your product or service so the recipient develops a sort of trust in you.  Personalization and engaging content are the two strong aspects of any newsletter.  Therefore make sure you use your newsletter as a powerful email marketing tool to propel your online business.