I'm really late to this post work, physical therapy and a lot of pain I'm trying to sleep off but this is pretty much how I beta. I read through once all the way through (or chapter by chapter for longer works). Then read through again and make notes on what worked, what didn't, things that really made me eeee, and what could be tweaked. One final line by line check for grammar errors and nitpicks (was John left handed two chapters ago and now right handed/had blue eyes and now brown, etc.)

But I also will work with people who only want the last part-a critical eye for mistakes. I like being flexible.