You will know what to say in your email newsletter once you understand its objectives.
What do you want your newsletter to accomplish?
Clearly understanding your objectives will help you plan relevant, useful content for your email newsletter subscribers.
Be deliberate in this. Write detailed descriptions of the content you need. Consistently focused, interesting content will build readership.
Eclectic, inconsistent content will be viewed as time-wasting, especially if you are marketing to businesses. If your newsletter doesn't consistently contain relevant, useful information, it will not be read.
If it isn't read, it will be a waste of your time and money.