Beta reading is the turbo-charger for revising a book. Finding beta readers and delivering a good beta is not simple, but there are practices and rules that make this important task easier to accomplish.
During my Workshop's in-person era, writers took on beta duties for each other, twenty pages at a time each month. We had three rules that were inviolate:
Make sure you note what you like.
Note anything that takes you out of the story.
Be polite and friendly.
You don't need a monthly group; in fact, reading in segments might make things a little harder. You could struggle to understand a book that you're beta reading twenty pages at a pop. Books improved in the workshops, and some even were published.
Authors' rules to succeed are simple, up at the top.
1. Exchange beta reads: Find someone who'll do a beta on your book, in exchange for you doing a beta on theirs.
2. Find one beta reader who's not a writer but loves your genre.
3. Use just a few betas, and set deadlines.
As a reader, make these essential for your betas.
1. Beta read in a genre you like
2. Read for story, not typos
3. A beta read is about the big picture
4. Measure the descriptions: too much, too little, just right
5. Read for continuity
6. Remember you’re not the author’s boss. Or the Spanish Inquisition.
That last rule is a part of the great column from Anne R. Allen in her always-useful blog. Read her post for the full advice.
You can pay for betas and get good ones, but finding one for under $400 is rare. I used a beta service from the UK for my novel Sins of Liberty, now in its final revision. Try as I might, I've never found another beta service that works outside of historical fiction. Six betas, $375. Quite the miracle.