If you could only give one tip to a newsletter creator, what would it be?

I'd say be transparent and keep it real. People do not like to be spammed AND to receive fluffy emails. So a newsletter should be friendly but straight to the point. We have to find the right balance between being informative and entertaining, so the content richness is a top priority. It's not bad if you don't follow a tight schedule. I'd rather wait to have enough content to send a newsletter, than just sending one every week with poor content.

Make unsubscribing as easy and friendly as possible.

Don't maintain regular schedule, readers will ignore the emails soon instead send the email only when the content is absolutely ready thereby maintain high quality (Applicable only to original content).

I'd say be unique. If a newsletter is just another variation of low hanging fruits (like "Daily top 10 from HackerNews" or "Weekly tech news") then I'm going to unsubscribe. Its not that I don't want to know these things, rather I don't want 8 mails daily with the same content in all of them. Once I see that there's repeititive content in my inbox, then I'm gonna unsubscribe from all except the best one (stuff like Hustle and Morning Brew are full fledged companies at this point, with professionals and thousands of dollars of budget they easily turn out to be better than what an indie maker can chug out daily)

Nice that sounds cool!

For me at Salt Sear Savor, I would say when first starting out to not overestimate the power of friends and family. Really lean on your personal network. Reach out to people you think might be interested, even if you haven't talked to them in years. And then directly ask a couple of those friends and family who are really excited about your newsletter to share it themselves.

Unless you have a mass following already, friends and family is how you get your first 50 to 100 subscribers. Or at least it was how I did :)