For a newsletter, any tips or advice for the publishing end of things?

I’m working on beginning a newsletter. I am considering using Mailchimp (the link opens in a new tab) for this and wanted to see if anyone has any recommendations on how to use Mailchimp or if another newsletter service is better, etc. It’s my first try to set up publishing announcements. Any tips or advice from the regulars that do this on how to know what deserves a newsletter’s attention and what to not announce but just post on a post or post on a page?