How do you become a beta reader?
People always want to know this! We have beta and gamma readers. Alpha reads are only my agent and my writing group. Beta readers are people from fandom who have proven that they know their stuff and are a part of the community. Peter picks these from people who are on my Facebook, who are interacting with him there, or who are on the 17th Shard. There's no promises you can get in on this. We do change it every book and get some new people, because sometimes we just want people to give fresh eyes on something.
Gamma reads, if you want to read things early, are bug hunters. They can spot a type form a hundred paces. If you are really good at finding typos, you can go to the thread on the 17th Shard, for every book there is a thread, a forum thread that talks about typos. And if you are consistently finding typos no one else has found, chances are good Peter will be like, "Hey, do you want to proofread for us?"
But don't feel like you have to do this because it actually diminishes the book a little bit, even though you get to do something cool, because it's not in its final form yet. I don't like beta reading when I don't have to, I'd prefer reading something with polish.