Do you review others' work? Beta reading can be a challenge, especially if the voice is way different from mine. When making suggestions for revision, I try to make no impact on the voice or the flow of the work.
A tremendous amount of time and energy can go into beta reading, but it is a critical part of getting your novel ready for publication.
1) Don't be snarky. It adds no value whatsoever, and will alienate yourself from your reading group.
2) Check for the fundamentals. Paragraph and sentence structure, punctuation, spelling. It is easy for a writer to overlook a lot of these, since the brain will often see what it meant to put on the page, not what is actually there.
3) Does a word or a phrase cause to stumble, or pause to consider the message it conveys? If so, it may be best to revise that passage.
4) Is there a natural flow to the story, or is it hard to follow?
5) Characters are harder to convey, but check to see if the character motivation and actions make sense.
6) Continuity - if a character is wearing a red dress, then falls down and rips her blue slacks, a continuity check is in order.
Good luck, and let me know if these tips are useful. I'd also like to know what you look for when reading others' work.