I'm always blown away by the ROI of user testing, so as I went through several rounds of it lately, I decided to take notes on things I did (or did not) that helped maximize that return.
I've organized those notes and put up a draft at: https://massimilianomirra.com/notes/getting-the-most-out-of-informal-user-testing-field-notes/
Would be keen to hear about your always do's and never do's when it comes to user testing!