Ask for feedback by promising not to take it personally. Give it by saying first that you care and want them to succeed.
The cover letter you keep tweaking. The book proposal. The business idea that eats so much shower time you forget the conditioner, again. Wouldn't you want to know if it's hot garbage before you bet years on it? Honest feedback is one of the most valuable gifts you can give the people you care about, and in a world where everything is awesome, one of the rarest. Norman Vincent Peale said most of us would rather be ruined by praise than saved by criticism. The fix is framing, so both sides know the honesty comes from care.
Two years out of college I was buzzing about a marketplace for local services. My peers cheered me on. Then I sat at a coffee shop just outside DC (I still remember the exact table) while a founder I looked up to spent what felt like hours explaining why the idea, and therefore I, would fail. Gut-wrenching. Years later I realized it was a gift. It forced me to understand the business more deeply and saved me from potentially years chasing an unviable idea. Now when founders ask me for feedback, I pay it forward.
Asking: "I would really appreciate your honest feedback - even if you totally hate it, I would not take it personally."
Giving: "I really care about you, and want to help you and this project be successful. So here's my completely raw thoughts - and of course, this is just my opinion."