I work at a school and we always lament at the shocking lack of communication. It has reached legendary levels but even when communication does happen it is often terse and can be taken the wrong way. I've been thinking about this with Beta reading. I'm usually quite harsh when I do Beta reading. I have to remind myself to point out the good stuff along with the buts that don't work. I recently did some Beta reading and I even pointed out the nitty gritty stuff and the author came back thanking me and I was thinking, I was a bit mean and now I regret that. So here are my tips that I have learned about giving feedback.
Don't be vague about your comments. This isn't helpful as you can't fix something if you don't know what is wrong. If you can't be specific then at least go into some description about why some section doesn't work or the mood that isn't achieved or the confusion you feel. I usually use the tracking changes in word and highlight sections and make notes.
Don't be personal
Never. Ever. Ever write something personal about the writer. First off that is so unprofessional. Even if you want to say something nice stick to commenting on the work because telling a stranger that whoever wrote this is a fantastic marvelous person you only manage to come across as creepy.
Highlight what is good
Every time I laugh or think 'wow what a pretty' line I stop, highlight it and then just a simple, 'I liked' this in the comments. Writers are people as well and we need to know what we are getting right just as much as the mistakes. Whenever you sit down to Beta read remember that you need to put in at least one of these. I use this also when I do reviews. I always pick out something that was done well. These books are their babies so handle with care.
If you do point out something that isn't right make sure you give a suggestion on how to fix it. This is a little what an editor does and this is a little more than what is expected from a Beta reader but this is a good way to give back. This is what I hated from my professors at Uni. They would tell me what was wrong but they didn't tell me how to fix it. In the end I stopped picking up my essays as they always had the same comments.
Stick to your genre
I hate it when people who don't like fantasy or romance read my books as there are certain conventions that are particular to these genres that you might not see in others. They always rag on certain aspects that I have purposely put in there. I used to see this on Critique Circle and other online writing groups. They need to critique others work before they can have their own work critiqued so they just look for something that is short and then rip into it without any idea or what is required in that genre. So far my best beta reading is from a group that work on the principle of service. No one needs to tell others to read others work as the people in the group automatically do so.
From experience I hate waiting for people to read my work. If I could I would be there leering over the shoulder asking them 'what?' every time they made a face. So return the courtesy and read quickly or at least as promptly as you are able. If you are rushed off your feet then send it back with what you have done so far. They can work with that and maybe you can finish the rest later.
Point out the obvious
It might not be obvious to the author. When you get too close to your work you can't see the mistakes. Our brain fixes it for us and we read what we want to see not what is actually there. So when you see a mistake and think, "They must know it is there." so we don't point it out. POINT IT OUT because assume does what it usually does.
Tip for the author:
Get a thick skin and send chunks not the whole thing. Remember that people don't love your baby as much as you can.