I was given the instructions by an Apple Genius when I went to inquire if I needed a new battery. This was 1 day before the $30 battery announcement. The Genius was making this recommendation before people paid $80 for a battery that they might not need.
Since I am working from memory I did a search on the web and I believe this article covers the proper steps:
This iMore article covers what you might lose with a clean install. Too bad I don’t see any link on how to do an clean install. https://www.imore.com/doing-clean-install-your-iphone-ipad-heres-what-youll-bring-over-and-what-youll-lose