Quick answer: You don’t. Or, at least, you don’t tell your friend their book stinks and then chat merrily about the weather or resume whatever else it was you were doing (celebrating their birthday, maybe — please don’t tell them this on their birthday). If someone you know is writing a novel, that means they still have time to improve it. If the novel’s already published, well, then I guess someone thought it was okay enough for other people to read, and you should probably shut up and congratulate your friend. The point is, if you’re friend is in the midst of writing, maybe they’re looking less for soul-crushing judgment and more for feedback on how they can make their story better. Here’s what’s actually helpful for them to hear: “Hey, I don’t like this particular thing, but I think you could make it awesome.” Not all critiquing is constructive. If your friend wrote a story about a dog and you hate dogs, then don’t say their novel sucks because of your personal preference. Plenty of other people like dogs and would read about them. Also, never utter the words “your novel sucks,” because that’s just petty. It will probably also make your friend do this:
Instead, try to figure out what you don’t like and why. Give them more reasoning than “it’s stupid” or “this is boring.” Maybe your friend needs to do more to endear the reader to their main character, or maybe they need to add more action and dialogue and lose some description. Find something concrete for them to work with. If you want, you can suggest ideas for how they might fix the problem, but keep in mind that the writer makes the final call. Readers are usually right when they feel something’s off, but that’s as far as their power extends. “This chapter needs work, but I loved this part.” Don’t just point out the bad things. Regardless of its quality, writing takes a tremendous amount of energy and dedication, and hearing someone rattle off criticism after criticism can be demotivating. Keep your friend’s spirits high by either starting out with a compliment (“This is a great idea for a story” or “I loved this character!”) or by taking a break from the negative and pointing out something you did like. It can be as small as a sentence or a descriptive image. Your friend will appreciate the mention and feel happy that you liked it. Basically, it tells them that if they keep writing more of that — the thing you liked — they’ll be doing a good job. “Don’t give up.” This must-watch TED Talk teaches an amazing lesson: You are not your novel.