Studied a lot of successful paid newsletters over the past few months. Here are some tips on running one

1/ Offer your best content free. This is your "sales" material. Direct new sign-ups to a sample of your best free writing.
2/ 85% of email reading happens on mobile. Optimize for small screens. Use images and rich media in moderation. Keep it simple and make your content easy to digest. Make it convenient to consume.
3/ Have a clear sell on your Subscribe page. Explicitly say what value your newsletter will provide. For example, "Subscribe to learn how to negotiate with your boss, co-workers, and customers" if you write a newsletter on negotiation tactics
4/ Write once, promote a million times. Each free piece of content should be re-posted on Twitter, Instagram, LinkedIn, Reddit, Medium, Facebook Groups, forms. Distribution is as if not more important than the actual content.
5/ Related piece on the Letterdrop blog: https://letterdrop.com/@wheres-my-audience/so-you-want-to-run-a-paid-newsletter