What are your tips after sending a first newsletter?

Hey! I'd love to hear from you some realisations / tips you have from putting together your First ever emailing (or like the first few).

What did you do to get the first one done?
What did you expect to happen, what was different?
What was very helpful?

• If you have been sending newsletter a long time, that is also OK. But most interested in people learnings after sending just a few.