Ah, peer review. Arguably one of the most important parts of the writing process, peer review is both a blessing and a curse to students and professionals alike. On one hand, peer review gives you a second (and often third and even fourth) opinion on your writing before you submit for a grade or for acceptance to a journal. On the other, for this aspect of the writing process to be effective, a writer needs to make themself vulnerable. Sometimes this hurts, especially when working with someone who equates "peer review" with "tearing a paper apart." (I've been there, it was embarrassing, but in the end I realized that not all of the feedback was useful feedback.)
Fortunately, peer review often isn't a showcase of your writing blunders but an opportunity to grow as a writer and perhaps even have a discussion about your writing. Not only can you learn where you have weaknesses in your writing, but you can also learn about what you do particularly well. The types of feedback you receive will change over time as your writing and the genres of your writing change. But as each piece and genre of writing has its own parameters, writers, professors, and editors too have their own expectations for peer review, something the peer tutors at my Alma Mater's writing center found out after talking to students and professors on campus.
Alhough most of us wish at least once in our academic careers that we had a rubric or checklist for peer review, having peer review guidelines clearly written up for us is unlikely. Regardless of the type of writing, there are a couple of guidelines you can use for any peer review situation.
Give friendly feedback. While you don't have to (and shouldn't) refrain from pointing out the weaknesses is another writer's paper, you also shouldn't tell the person their writing is awful (even if it is). The goal of peer review is to make better writers, not just better papers. So while it might feel like you are critiquing the writing, you should use peer review to focus on... well... your peer. Do you like being told your writing is bad? No? Then don't bring that into peer review.
Tell the writer their strengths. There are two main reasons for sharing strengths with other writers. First, it feels good. Starting out with a compliment sets a good tone for the rest of the feedback, no matter how much (hopefully constructive) criticism follows. Second, as writers, we are our worst critics, so sometimes we cannot see our own strengths. By pointing out the strengths in a paper, you help the writer see what pieces they should definitely keep as well as encourage good habits.
Focus on higher-order concerns first. In the world of revision, higher-order concerns are things like organization, content, and "flow" (a writing characteristic that we all know but for which we don't really have an explanation). Without these, a paper is nothing, no matter how perfect the grammar and mechanics. In contrast, lower-order concerns are things like grammar, syntax, and spelling. While a good paper has these things, they usually won't contribute to making or breaking the argument of the paper. This isn't to say that you shouldn't help out your peer by highlighting grammatical errors, but these shouldn't be the focus of your review. Furthermore, if your peer incorporates your feedback, those grammar errors you point out might be deleted altogether. Point them out, but make sure you give more weight to content and how it is presented.
Be timely. In the event of coursework, the time you have to review a paper might not be up to you. When reviewing an article submission to a journal, however, there is likely more leniency. While being prompt (i.e. returning a paper plus feedback within six, or better yet, four weeks of receiving an article to review) doesn't guarantee other reviewers will do the same for your submissions (often reviewers for journal articles are kept anonymous), it doesn't hurt to rack up good peer-reviewed karma.
Explain your feedback. Merely circling a phrase, crossing out lines, or drawing arrows all over the place isn't particularly helpful. There are some conventional symbols you can use without explaining yourself (e.g. "sp" above a word means spelling; a caret "^" indicates something needs to be inserted), but if you have your own set of correction marks, consider including a key. It is also helpful to type up a summary of your feedback, highlighting what you think are the most important things for the writer to consider when revising their paper. If you have an opportunity, for instance via in-class peer review, to talk directly with a person, start up a discussion about feedback! Foster an environment where reviewer and writer alike can ask and answer questions, turning what can often be a back-and-forth exchange of drafts into an informal collaboration.
Consider your reviewing tools. If you are giving feedback in Microsoft Word, use the Track Changes feature. Most word processors include a comments feature, so use that to make suggestions directly where that feedback is applicable. If you are providing feedback on a hard copy of a paper, think about using a pen or pencil in a color other than red. (A 2012 study suggested that feedback in red is more likely to elicit a negative response. I prefer green myself.)
Do unto others.... Finally, think about the types of feedback you would want, again trying to build up that peer review karma. Chances are, you want feedback in a friendly tone (although there are instances where this might not be crucial i.e. the tenth draft you sent to your advisor for review), and you want honesty. Don't tell someone there paper is perfect (unless in some rare event it actually is), but don't overdo it on the criticism (if everything is wrong, pick a handful of things that you think are the most important items to address).
Peer review isn't always easy, and it isn't always helpful. Hopefully, though, you can critically assess another's writing to help them improve how they communicate. And who knows? You might learn something about writing yourself in the process too.
Have your own ideas for peer review? Hit up the comments section to share your experiences.