This is the golden rule of workshops. While novelists might get a pass (because we generally assume their works are entirely fictional and not based on their lives), poets and memoirists are often under fire not because of their syntax or sentence structure but because of the content of their pieces. Any feedback you provide should remain focused on the writing as it is presented to you on the page. Compliment a lovely turn of phrase or point out a passage which could benefit from greater syntactical clarity. But steer clear of giving unsolicited advice.
By attending a workshop you are signaling that you are committed to giving and receiving feedback. It can be hard to give meaningful feedback if you try to rush through reading a piece on the spot. You don’t necessarily need to provide a thorough line-edit of each piece you encounter, but it will be helpful for the writer if you comment on elements of the piece which are working (and some which need improvement). Writing these down ahead of time helps! The key is to make sure you are giving as much to the group as you are receiving.
A great poet and mentor always stressed during our feedback sessions, “I’m only one reader, other viewpoints may vary!” Keep in mind that all feedback is take it or leave it. Some critiques may resonate with you more than others. Not everyone will understand your work or project. But hearing diverse points of view is always important. After all, we’re ultimately writing for an unpredictable audience. It's good to know what to expect once a piece is handed off to readers.
Let your fellow workshoppers know what kind of feedback you’d like to receive. Are you looking for line edits or more structural feedback? Are there particular sections or concepts you are struggling with? A particular phrase? Telling your readers what type of feedback you’d like will help the group/reader stay on track and help you get the most out of the workshop. Adding a short note to the top of your draft helps everyone to be on the lookout for as they read and respond to your piece.