Writing a peer review for a fellow writer is a very specific rhetorical task. You have an audience--the other writer, a purpose--to help them with their writing in specific way, and a way of communicating--either in writing or by speech. Like any communication act, however, things can break down. Your advice, like anything written or said, may not be clear to the writer, or it might not be accurate.
Therefore, for any review you give--or receive--a good step to always include in the process is a review follow up. You can do this in a number of ways:
You can, upon receiving the review, read through it or listen to it, then discuss it with the reviewer. Ask questions, say it back to them to make sure you're getting what they say, try putting it in your own words.
If you exchange reviews by writing, think about the review and then write back to the reviewer to let them know how you used their advice and why.
Show the reviewer a revision you made based on the review given to you. Explain how you came to make the changes you did.
If the review is simply not helpful or not what you asked for, politely let the reviewer know that. Give him or her a chance to explain the review or to revise it. Remember, reviews are not always easy to write, and like any writing, they may need revision as well.
The Benefits
Talking and thinking about reviews with the reviewers helps you:
Think about the reviews more fully.
Use the reviews more effectively.
Write better reviews for others.
Using this Activity to Revise
Simply put, understanding what a reviewer offers makes it easier to decide how to use the review, and thinking about how you might use the review helps you view your writing from a bit of distance. The perspective helps you think not only about your writing, but about your own habits as a writer. It helps to create a dual focus: one on the written product, and the other on how you write, how you work as a writer. Knowing the interdependence of how you work and what you work on will make you a better writer, which in turn will lead to better writing by you.