Writing for email is harder than you think
It sounds simple—you have information you need to convey to your constituents, so you write something up and put it in an email. It's not that hard.
Except it turns out that it is hard. Doing it well, at least, is hard.
Keep your content short
The first big consideration is how long your email is. The average time the average person will spend reading your email is between 15-30 seconds. If your content is longer than 200 words, it's nearly guaranteed that your content won't get read. Paragraphs of content should not be longer than 3-4 sentences.
Use headings
To make your email easy to scan, it's highly effective to break up your content into headings. See the above headings for "Keep your content short" and "Use headings"? That made it easier for you to scan this web page. Email is similar. The email framework has great hero headline content blocks for you to break up your content using headings.
Have a purpose
Nothing is worse than getting an email and not easily being able to determine what you're supposed to do with the information you're reading. Keep this front and center for your constituents—what do you want them to do? The key takeaways and call to action should be extremely clear, and the content should all support that single purpose.
Write clear subject lines and preheaders
In order for your email to be compelling enough for anyone to even open, you have to catch their attention in their inbox. They don't have to open your email.
The subject line appears just below the From name of the email. It needs to be short due to space constraints—40 characters maximum—and give the readers a very clear idea what your email will be about.
Your preheader is the additional text the reader sees below the subject line. If you don't have one, it will begin with the text of your email, which may or may not work. Writing an effective preheader can help give important context to your message, especially if you can't convey everything about the topic in your subject line. Keep these to 40-130 characters.
Consider voice and tone
One surefire way to lose your audience is if your voice and tone doesn't match the topic you're communicating about. Think about voice and tone like the personality of the content: how do you want the reader to feel? Supported? Excited? Anxious? The words you choose matter when you write.
For example, an email inviting the constituent to a fun event should have a voice and tone that conveys excitement or celebration. By contrast, an email about important financial requirements should be serious and to-the-point.
Further reading
This great article by Litmus covers email length, accessibility, and how to write simply.