If you want to know what beta readers are, read this post: Revise Your Book: Beta Readers.
As an example of how beta readers work, I’m going to list my own experiences here.
Victim: Unlucky soul conscripted into the ‘read drafted manuscript’ army.
Stage: What stage of the drafted manuscript they read.
Format: How they read and respond.
Content: The types of comments they make on my work.
Timeline: How long it takes to hear back from them.
Verdict: What my overall impression is of our time shared, and also if it was overall successful.
Victim: Maw (mother)
Stage: While writing. I ranted and complained and mused and pensively grumbled about where I was going next.
Format: Vocal. I read it to her while she very kindly drove me to and from college when I came home on weekends.
Content: She said things like, “That character wouldn’t know about the plot to dethrone the king,” and “I’m not sure I understand what’s going on here,” and “Keep reading! You’ve read everything you have so far? Then keep writing!”
Timeline: Instant Gratificationnnnnnn! It’s a beautiful thing.
Verdict: My dear mother is the person who validates what I’m doing. It’s important to feel validated, especially when you feel like it’s taking absolutely forever to finish this scene. I will always continue to read to her or have her read my early WIPs (works in progress), because I enjoy, depend on, and adore the encouragement she provides.
Victim: Lister (twin sister)
Stage: Early draft.
Format: Printed. Lissa likes to have a hard copy. To save trees, I print double sided, single spaced, and I let her deal with the issue of having enough space to write comments.
Content: She does a lot of line editing. She has an eagle eye for typos and syntactically nefarious sections. She puts a lot of notes when she likes what’s happening too.
Timeline: A couple weeks (when she actually sat down and did it). Lister is a fast reader, but it does take her a bit longer to read while she’s constantly editing and marking with a pen.
Verdict: She’s a good resource, and had some wonderful and insightful comments, but she was busy at college and so it took a while for her to actually get started. By the time she gave back the hard copy, I’d already made a lot of changes to the ms. I don’t know if I’d ask her to read it unless I was sure that she could read it in a reasonable time.
Victim: Seena (oldest seester)
Stage: Middle stage draft. She was happy to read it, but she really didn’t thrive in the editing process until later drafts.
Format: Kindle comments. Kindle/Amazon allows you to send documents to your kindle for free (with wifi), and it’s a handy way to send someone your book. Once she put the comments (notes) on it, I could redownload the drafted ms from the archive and have all of her comments on my own kindle.
Content: She is excellent at plot holes. She notices everything, and she points it all out.
Timeline: It took her almost six months to sit down and start reading it (she can’t read books out of order, so she had to finish reading the entire Riordan series before she’d lay eyes on my draft. Once she started, she didn’t stop though. She got through it in a few weeks.
Verdict: Not so good if you want feedback this century, but the critiques she gave me were very helpful for overview revision.
Victim: Tifren (best friend)
Stage: Late stage draft. This had more to do with when I asked her. When I finally
Format: Kindle / Text messages. She read most of it on her phone Kindle application. She would send me a bundle of twenty text messages with the comments she had throughout the chapter.
Content: She was excellent at recognizing when sections didn’t make sense, and picking up on the themes and overarcing plots I wanted to accomplish. She helped me polish it up, suggested chapter breaks where necessary, and pointed out when I used complicated diction. I made a lot of major changes based on her suggestions.
Timeline: It took her a couple months to read through it (we were graduating college and then amidst summer activities). Yet she sent me the comments on each chapter as she read them, which allowed me to edit in tandem with her suggestions.
Verdict: An excellent resource, with a helpful and unique perspective. I would ask her to read again, but probably middle stage drafts, because I would love to see how her feedback affects my writing earlier on in the revision process.
There were other people that read my book.
Collateral Damage Victims: Grams (grandmother), Treven (guy friend), Brosh (guy friend), and Cau (aunt). Those people were a mixture of pat-on-back-ers who either didn’t like it (early draft issue), or who I hadn’t asked to give feedback, and Shruggers who read earlier drafts out of pity or didn’t care for the genre (fantasy).
Overall, you have to find people who want to read your book, and who can offer you the type of advice you want.