I know you may not be a writer, but everyone must give feedback at one time or another. If you have had to call customer service for anything lately, "remain on the line for a short survey after your call" should be familiar. Or the cards left at the tables at restaurants. Whatever it is, everyone is asked to give some form of feedback for something in their lifetime.
But many people look at the chance to improve something in their life like a chore. Like the place? All 10's! Had a single bad experience after years of fantastic service? All 1's! For the love of all that is holy, don't do that. Just don't. It is lazy, dishonest, and stupid. If you aren't inclined to make the effort, then just decline the request. You hurt no one by doing that.
So what if you want to give constructive feedback, but aren't really sure how? Well, now I can help you out there! Here are some guidelines to follow.
Don't commit to giving feedback and then not do it. That includes saying you'll take the survey and then hanging up. Or telling a writer you'll read their book, review it, and then forget it. Or getting a freebie at a concert in exchange for a blurb online. If you don't have time, then just say "I'm sorry but I will not have time to do that today." No harm, no foul.
If you commit to it, do it in a timely fashion. That doesn't mean you'll get around to it this summer, over Christmas break, or eventually. Keep in mind the ideal time frame is different for different projects. Use a little common sense and you will be golden.
Ask what kind of feedback is needed from this project FIRST. Don't read a book, making notes about every little error and detail when all the writer wanted was content feedback. Don't write a dissertation on a local band's live CD when they just want a blurb for Twitter. Find out the details first and you'll save yourself some time.
Start with a positive and end with a positive. I'm serious about this. No one wants to hear "Everything is bad, bad, bad, bad!" when a "This is great, although this, this and this need X. That last part was fantastic though, really reminded me of Blah." is so much better to hear. If you are in this just to be a heartless bitch or raging asshole, just decline. For real. Balance what you like about the project with what you don't like/what doesn't work.
Do not lie. I don't care if this person shares your lifeblood and you have pinky promised to be best friends for the rest of your damn lives. If it sucks, be honest. Because someone else will and then your "friend" is going to want to know why you did such an unfriendly thing as lying to them. It doesn't help someone improve their craft when you make everything into rainbows, butterflies, and unicorns when it shouldn't.
I have been very fortunate to be surrounded by amazing people that have given constructive feedback. I may not have always liked the feedback, but it was good feedback. It was real, it was constructive, it was good. I have had several people take me up on an offer made two weeks ago for a free copy of Journey of Shadows in exchange for an honest review. JoS is about 200 pages long so my expected time frame for that is about a 1 month turn-around from the time of receiving the copy. Two weeks to read and two weeks to write. That may or may not be logical for a 83k word novel, but I think it is reasonable. Some folks would read that in about 48 hours and could review it within another 24 hours. I probably could if I had the time. But right there is the problem that so many folks find familiar. The time is important. And it is in short supply!
Give good feedback folks. It is designed to be helpful. Don't make it harmful instead!