1. Make sure the comments are appropriate for the purpose. I do see people who put comments in reviews that have nothing to do with the story or their opinion of the story itself. I have seen it, if you haven't seen it, you will.

When you write your own reviews, try to make your comments appropriate to the story or the author. This can take many forms - maybe the story reminded you of a story of your own and you want to share it with the author, or you want to tell the author they are awesome and that is why you are still reading their things. Of course, giving your opinion on the story and offering suggestions also would fall into this category.

If you have other things to tell an author that have nothing to do with reviewing itself, or nothing to do with a particular item, an email might be a better form of communication.

2. Rate appropriately. I have seen very low ratings given for no good reason (thus the title of the newsletter), and I have seen high ratings given to items that, in my opinion, likely still needed some improvement.

As far as this goes, I think what we all need to remember is... reviews and ratings are someone else's opinion. We don't have to agree with them. However, something that we should all watch for is that we make sure our review and our rating match.
If we've got a lot of edits to suggest for the author, it shouldn't be rated with 5 stars.
If we've got no edits to suggest and we loved it, it shouldn't be rated 3 stars.
And so on...

3. Keep it positive. Remember that text has no feeling. Unless you are writing completely in emoticons, someone is not going to see your teasing smile at the end of a teasing sentence. Be sure you keep everything positive, and when reviewing (unless reviewing a very good friend that knows better), keep your criticism constructive. There is a very large difference between, "Your grammar sucks," and "You may want to take a look at a couple parts of grammar," and then offering suggestions.

4. Despite what people say, there is no minimum or maximum length. Sometimes, all there is to say is that it is amazing, and it brought a tear to your eye. There is no requirement to elaborate. But please do, do, do let them know how you felt after reading it. If it didn't catch your eye, that is something they need to know just as much as if you loved it.

5. Be honest with yourself, and with the writer of the item you are reviewing. Read the item all the way through. Give an honest opinion, so the feedback is valuable. If you couldn't finish it, but are sending the review anyway, let them know what stopped you from being able to finish it. If we are not honest as reviewers, we are actually no help to those we are giving feedback to.