Do you use beta readers?
How does one go about becoming a beta reader?
I don't use a beta in the classical sense. Two friends of my read chapter by chapter as I work, and basically if they keep asking for more, I know I'm on track. They're my nudge when I start to slow down, but I don't do hard editing or story work until the first draft is done. Then the draft goes to my agent, and her notes are the first I take for major revisions.
As for becoming a beta, I have zero idea. I don't beta for anyone, so I don't really know that world. I assume just having friends in the lit circle, maybe joining a writer's group, or tweeting about wanting to beta can go a long way!