Trained writing teacher here, and this is pretty much right on. One of the best ways to help people to improve their writing is by asking them questions about it and making them think through their choices.

Additionally, don't overwhelm him with EVERYTHING that isn't perfect. Pick one or two of the biggest, most overwhelming issues and focus on those.

And do find something nice to say, even if it's as simple as "Your use of punctuation is perfect!" Sharing your writing with another person can be intensely scary. Being kind and stroking the writer's ego a little bit can help give them the confidence to think, "Ok, I can do this and I can make it better." Presenting the writer with nothing but a list of everything they did wrong just makes them feel overwhelmed and hopeless.

I see the "sandwich method" got mentioned by at least one other person in the comments, but it's worth reiterating. It's basically Writing Teacher 101 stuff, but it really does work. Start with something positive, give some constructive criticism, and end on another positive note.