I've learned quite a lot about editing from "Style: Lessons in Clarity and Grace." It presents some tricks to restructure and improve the flow of sentences, and through that process, to generate the momentum to really think about what you want to say.
[1]: https://www.amazon.com/dp/0134080416?tag=duckduckgo-d-20&lin...
EDIT: link to the book: https://www.amazon.com/Style-Lessons-Clarity-Grace-12th/dp/0...
* Reading lots of books on writing. Probably this (https://www.amazon.com/Writing-Web-Creating-Compelling-Pictu...), definitely this (https://www.amazon.com/Style-Lessons-Clarity-Grace-12th/dp/0...). Got both from local library.
* Reading lots of other books I got from library (on writing and marketing).
* Practice, coupled with observing results on google analytics.
* https://practicaltypography.com/typography-in-ten-minutes.ht... for basic design.
* Free content on https://stackingthebricks.com/ (there's a lot, although it's mostly lead-in to paid content).
The last one in particular motivated me to write based on research, which resulted in massively improved results.
https://www.amazon.com/Style-Lessons-Clarity-Grace-12th/dp/0...