Even a beginning writer (or well informed reader) has something valuable to say. Writers need to have an idea of how readers will react to their work, and, unless you're writing for specific academics, it isn't likely that the average reader will read your fiction with the same critical eye an experienced writer. Think of the critiques you receive as a public survey on your work. Some comments will be from writers less experienced than yourself and some will come from more experienced writers. You, as the author, are the final judge of a critique's value.

Use tact in your feedback. We communicate entirely through text while on-line. We don't have the benefit of vocal shifts, smiles or raised eyebrows to help communicate our thoughts, so we must choose our words very carefully. It is very easy to be misunderstood on the internet. One of the most useful words in a workshop is "consider." Rather than saying, "I think you should change this part because it is confusing,." you could say, "Consider changing this part for clarity." The later wording leaves the author with a better sense of control with additional options. The best critiques inspire the author to look for creative solutions and more effective alternatives.

Do not write the work for the author. It is very tempting to inflict our own ideas on an author in our critiques. It's a natural impulse for writers, but one we should curb if we are to be helpful. So avoid comments that give specific story changes. If there is a characterization or plot problem, it is better to simply point it out and explain why you had a problem with it.

Be specific. It is of no value to simply say you like or dislike something. Saying "Awesome!" doesn't help a writer grow. We need to know why it is awesome so we can do it again. If you don't like something, try to determine why. For example, if the hero does something you don't like, it is better to tell the author, "The hero seems to jump out of character at this point. Earlier, on the 4th paragraph, he said this and did that, then in the 12th paragraph this happened. Is this what you intended?" Also be specific about your favorite scenes, lines and descriptions. Especially the most memorable ones.