I know how very few people comment, much less provide criticism on stories online. Giving criticism, however, easy for the reader and helpful to the author.
This guide isn't just for stories, I've found it useful in almost anything I've ever read, watched or played. In fact, I've even used it on food. That's just how versatile criticism can be. However, for the purpose of this guide, I'll focus on stories.
Many people reading this might say "I gave you criticism. I said it was good!" The problem is, that this is bad criticism. I know, you said it was good, so that's positive, right? Wrong. No matter whether you're giving good or bad criticism, a simple "good" or "bad" is bad criticism.
Sure, a nice "This was good" is a positive comment, but as criticism, it's bad. The point of criticism is to express your opinions in detail. If a story is good or bad, it benefits the author and the readers if you explain how it's good or bad.
For instance, on my most recent story, I received this comment: "The chapters have gotten too short and sloppy." Let's break that comment down.
The chapters being too short is the best part of that comment. It explains exactly what's wrong to the author: now I know that for the enjoyment of my readers, it would be a good idea to try and lengthen my story chapters. Maybe not all of them, since the occasional short chapter isn't a bad thing in most people's eyes. Now I know what to do about this aspect of the comment.