That is what your beta readers are, most of all – a reality check. Tell your beta readers not to worry about copyedits (or that’s all you get) but to concentrate on whether the story makes sense, catches them, and fits the genre.
The reality check works on two levels: first, you just spent at the very least months working on this story. You’re too close to see if it comes across as you wanted it to. If you’re a Putter-Inner like me (meaning you add things as you revise) you might have destroyed the story line and not be aware of it.
The second level is to see if your story fits the genre conventions and is not reinventing the wheel. My husband, who is more patient and a better person than I am and who reads more than I do – mostly due to having more time – often picks up free books on offer from Amazon. He then proceeds to make comments while reading, and to ask me to read the more egregious portions.
Nine out of ten of the worst offenders in books are clearly people who are reinventing the wheel. Say, someone writing science fiction as though no one has ever written an alien race before; someone writing fantasy as though no one ever wrote magic before; or someone writing romance as though they’d never met a live human being.
Every genre has certain things you don’t need to explain, because everyone gets it. No reader of science fiction, unless he’s three years old, needs a lexicon to explain “Spaceship.” (Yes, there are books with this type of lexicons.) And if you start your book with a disquisition on alien linguistics, the average science fiction reader is going to be mighty upset if there are no aliens in the rest of the book.
Betas must have two characteristics: they must be voracious readers; they must read in the genre you’re trying to write.
Both are very important because a lot of our “how a story is put together” is subconscious, as is our knowledge of genre conventions.
Unless you’re deliberately trying to hit a retro market, they should be readers of recent stuff, too. For instance, any reader of romance who only reads pre-seventies romance (me, me!) is likely to tell you that you’re writing porn if you give her something that’s targeted at today’s market.
Beta readers aren’t usually paid. That means you should have at least ten, if you want to get answers from six. Inevitably, someone’s llama will get sick and someone will have to wash her hair. Don’t be offended if you don’t hear back. Mostly it’s real life interfering. But also some people are bad at reading things when they’re told to. Let it go.
When you get the results back – supposing that all six don’t tell you “Good Lord, you think that’s a novel?” – ignore anything only one or even two readers mention. (Unless it’s something like “from chapter four on, you have duplicate cars,” which I did in one book and only one beta reader – Hi Francis! – got.) Unless three agree it’s not worth considering. Of course, if all six agree (and you’re sure they haven’t talked to each other) you definitely should consider the change.