What to send to (and where to find) beta readers

Putting your early manuscript out into the world can feel fairly scary (and exciting!), even if it's only for the eyes of a handful of happy, helpful beta readers. But a book-in-progress is a profoundly personal thing, and we seem to have a way of winding ourselves into knots about anything and everything related to the source of that fear. And so we start overanalyzing something as simple as sending a link to an eager, would-be reader ;)

If you're feeling the uncertainty, I offer three reassuring truths:
  1. You don't need to find so many beta readers (3-5 engaged readers per version is a good target, although that might require inviting 12-20 who seem qualified and interested)
  2. You don't need to turn into any sort of pushy promoter, and you can be quite casual and natural when requesting readers' help (see below for a few real examples)
  3. The very best beta readers are the exact same people who would actually want to read what you're writing about, so you won't have call in any huge favors or force anybody to read anything that they'd hate

Still, there are indeed a few impactful, tactical bits that you may as well get right. Right?

Direct outreach when you're starting from scratch, without any audience

Well, to start with, you're almost certainly not starting from *scratch*. If you're writing a book about it, you probably know at least a handful of other people who are interested in the thing. So to start with, forget about scale; maybe just ask those people?
I followed this approach to start beta reading with my (seemingly forever in-progress) fourth book, and it worked a treat. 
My rule was simple: each morning, I would think of one person who I knew, who might be keen on the topic. And then I sent that person an individual message, like this: 
Hi Alex, I recall you saying a while back that you were deep into thinking about X (or starting to learn about X or whatever).

I know this is kind of out of nowhere, but I've been working on a book about the topic, with a focus on Y and Z. The manuscript is still super early, with loads of problems and rough bits, but if the topic happened to be relevant to you, I'd love to send you the current draft and see where you get stuck ;).

Absolutely zero pressure, of course -- I know you've got plenty on your plate.
I sent one note like that each day for two weeks, and suddenly I had more than enough feedback for me to figure out what was working (and what wasn't).

Using public content to bring interested readers to you

If you'd like, you can cast a wider net for beta readers by "working in public." 
One approach I've used (repeatedly) is to repurpose ideas and excerpts from the book-in-progress as public content, which each include a little call-to-action for beta readers.
For example, I'm currently writing about "outcome oriented communities." So at the end of each article or video, I write or say something like:
By the way, I'm also working on a book about this topic. The manuscript is still a bit of a mess, but if you'd like to get in there ASAP as a beta reader, I'd love to have your feedback. Just email book@robfitz.com and I'll send you the link once it's ready.

For a concrete, actual example, see the conclusion or this article and/or this video (the video's beta reading call-to-action is at 8:23). 

Is this "optimal" in a marketing sense? Not even close. But does it generate enough interested readers to keep the beta reading moving? Absolutely.
PS. You'll note that my call-to-action in these examples isn't a fancy form or website, but a simple "email me." Whenever one of those emails arrives, I say thanks, send the manuscript if it's ready, and tag the contact as a potential beta reader for future reference.

Recruiting readers from an existing newsletter, audience, or list

If you've already got a list, the most important consideration is to avoid burning it out all at once. 
Firstly, this is because not everyone on your list will be keen on the book, and not everybody who is keen on the book will want to deal with the messiness of a pre-launch, beta reading manuscript. (Some will just wait for the finished, polished thing.)
Secondly, this is because you'll likely run multiple rounds of beta reading, and it's quite convenient if you can treat your list as a steady drip of readers, as opposed to a feast-then-famine.
My preferred approach is "borrowed" from the way that Arvid Kahl filtered, invited, and nudged the beta readers for his two books. Here it is:
As part of a regular newsletter or communication, let everyone know that the book is in progress, that you'll be doing several rounds of beta reading, and that, if they're interested, you'd really love their help and input.
Within that message, include a link to a brief form that allows them to filter themselves by the early-ness/roughness of the version they'd like to review. 
Arvid asks would-be readers to filter themselves into three tiers of eagerness:
  1. "I want to be an alpha reader" (super rough version, likely with loads of problems)
  2. "I want to be a beta reader" (more organized, more coherent, but still tons of typos and unpolished prose)
  3. "Just let me know when it's nearly finished and ready for early access or pre-order" (a finished book)
The actual request can be disarmingly simple. 
Here's the full message that one of our community member used to get 163 beta readers (i.e., far more than needed) from a list of 12k blog readers:  
Hello _____, greetings from Baden Württemberg,  

I’m writing to say I won’t be writing these weekly emails in August.  

Instead, I’ll be working on my book. (Guess what? It’s about growing startups). 😏  
And I could really use a few “beta readers” to look over chapters and provide feedback. If you’d be up for providing some feedback, fill out this form to let me know?  

Many thanks! 🙏🏼
Nothing too fancy, right?
The survey itself was fairly straight-forward: a few questions about roles/goals/experience and then this lovely segmentation question:

Once you've identified your interested/qualified potential readers, you can just directly contact a group of them each time you're ready for more feedback:
  • Expect about a 25% conversion from stated interest to engaged reader, so invite 20 (who have already expressed interest) to get about 5 who actually leave meaningful feedback
  • If you're trying to stretch your list, then email only 12-20 people at a time; whenever you need more, email another 12-20.
Of course, not every author is happy with a 25% engagement rate. 
If you want to nudge for a bit more input, you can send a reminder with a soft deadline. Arvid phrased it something like this (Arvid's structure, my words -- make it your own!):
Just a quick note to say huge thanks for the support, and to let you know that this round of beta reading has been hugely impactful. We've already received XXX amazing comments, and it's helping so much to make the best book possible.

If you haven't had time to get your feedback in, you've got until this Friday the Xth (the link is still the same: https://helpthisbook.com/...)

Or if you had hoped to contribute but haven't been able to find the time, fear not -- I'll be running another round of beta reading in a few weeks (once I've worked all this feedback back into the manuscript), so there's still another chance for you to get involved if you'd like to. Thanks again!
When nudging, just be careful not to "force" people into leaving feedback by calling in any big favors or demands. The problem with being pushy isn't that it can backfire and burn bridges (although that does happen also). The bigger problem is that you're muddying your own data by gathering a bunch of feedback from people who didn't actually want to read the thing. (What good is reader feedback from people who aren't your actual readers!?) This is why you also have to do the hard work of putting yourself out there instead of relying exclusively on friends, family, and professional editors.

In conclusion 

Keep it casual, keep it human, keep it simple, and put it out there! 
If in doubt, start small, personal, direct, and get fancier from there.
PS. Find an approach that works brilliantly? Or finding yourself totally stumped? Either way, let us know in the community. (You have free access to the authors' community as part of your helpthisbook