You know you need beta readers. You need all kinds of partners in writing. Crit partners, writing groups and beta readers. You need them because you aren't perfect. You make mistakes and, when writing, you become blind to your own fails. Writing partners give you a chance to get inside your reader's head before you unleash your creation on the world (whether that world is an agent, a publisher, self-pubbing or your grandma.)
I've had enough experience in beta-ing and being beta'd to offer this short guide to beta reading (or giving any kind of feedback.)
1) What Do You Want?
Know what you're being asked for/asking for. Beth Revis has a great post here that goes into deep detail - not only Alpha, Beta and Gamma reader definitions, but also, what point in your writing you'd need any one of these. Know what kind of read you are asking for or you're being asked for and you won't be disappointed.
2) A Great Beta Read...
...Is like a conversation with your book. The comments aren't all smiley faces and 'like it'. They need to ask questions, test your logic, poke holes in your plot. The best beta reads I've had do that. I argue with the comments my readers make and sometimes they'll suggest something so obvious (which I left out) and such an elegant solution for putting it back in that I sit back and say, DAMN! (This just happened to me with the beta read I got from Jenny Herrera. That girl is smart.) Be the beta reader that gives THAT kind of care and attention to the work. Even if you think the comment might hurt a little, or if you think the writer was doing something on purpose. Err on the side of over commenting and put down every time something (good or bad) occurs to you. You wouldn't believe how many times one comment, one question shifts the whole meaning of the draft for me. Crystalizes it in a really good way.
3) Take the Time
To read and comment, it takes time. Beta reader's need to not only read and comment but think and digest your story, interact with it. I am guilty of being very impatient when my book is out. I am a beta reader stalker, having to sit on my hands to keep them from emailing, "Well? So? What did you think?" By the same token, when you are reading, take the time to do it properly (even if you are being stalked by the writer!) A bad beta read is one (and I got this once) that has few comments and a one paragraph sum up at the end that says something along the lines of 'Great Job! Really liked everything about it. I can see it on the shelves already. You're the Best!" Unless you are in Middle School, this kind of praise is meaningless. You know you aren't the best and that your ms. isn't perfect - that's why you sent it to the betas. So don't be a sloppy beta reader. It's not what you want in return.
4)WHAT TO DO IF YOU DON'T LIKE THE BOOK.
This is tricky, tricky. Firstly, you should know the writer you are beta-ing for to know if you like or respect their work (generally.) If you don't, why are you offering to beta for them? Secondly, you don't have to like the book to be constructive. Art is subjective. All you have to do to be a good beta reader is to respect the writer and to respect the craft. If you can do that, you can beta anything. I'm not a super huge fan of romance as a genre (though when I was a teen, I read every single Jude Deveraux book there was. Twice.) But I can beta romance because I can respect the writing. I look at the work, not as a reader, but as a writer. I can see where something is working well and where something is confusing. I don't have to like pirates or time-travel or zombies. I just have to respect them. (Actually, I love time-traveling zombie pirates, if anyone has such a book for me to beta, I'm in.)
That's it. That's my guide. What did I miss? What do you look for in a beta? What do you bring to the table when you are beta-ing?