Even if you see flaws in a person's writing, do not be as harsh or quick to point out their mistakes. Everybody makes mistakes. It's what makes you human and to be human is to err. Keep this in mind if you see something that does not make sense in another person's writing; what you could do is leave a helpful review pointing out the mistake and leaving suggestions on how it can be fixed.
Rememeber your tone!
Going hand-in-hand with being positive, things you can say over the Internet can be mistakenly misinterpreted into something that wasn't meant to be; for instance, your light and airy tone can be taken for sarcastic and that could hurt a person's feelings. Sometimes by starting off with "no offense" can really offend a person because you may sound insincere when saying that.
Remember, any writer who has taken the time to seriously write and share on the site will be sensitive to feedback. It may take a lot of courage for that ONE author to post just one story and can take only one bad reviewer to trample on their self-esteem. Therefore remember when you go into a story and want to leave a review, that it is impossible to expect an author to become emotionally detached from their work.
Broad reviews like, "This is great! Please update!" are aplenty. Merely telling somebody to update is very selfish so try to avoid being that person. To leave feedback is to help an author improve and can certainly be more useful in giving you, as a reader, a lot to look forward to. This in turn helps the author know what their readers like, why something works and why it may fail. If it helps; keep a list of strengths, weaknesses, concerns, and suggestions for your author to leave in the review.
I find that when I read anything of Dot's and especially if I like it, I keep my notepad application open and write along as I am reading. Dot's method is similar: First she reads the whole story, then goes back to write down tips and suggestions as she is re-reading. Of course, there is nothing wrong with a little praise; this goes along with the strengths and everybody likes to hear how well they're doing.
Thank you for taking the time on reading this short article. Hopefully if gives you a better idea of what to look for when you are leaving feedback and how to do it.