One of the best ways to improve your newsletter’s design is by looking around you. You’ll probably find that you come across newsletters in your daily life fairly often.
When you find an example of a newsletter you like, save it. A collection of samples like this is called a “swap file.” From time to time, pull out your swap file and go through your samples. Pay special attention to what you like and don’t like about each one.
You don’t need to be a professional designer to know what works and what doesn’t. Often it is just a feeling. But if something appeals to you, it will probably appeal to your readers too. Stick to the basics of good design and do what looks good, and you are sure to have a winning newsletter!