Last year, I posted the comment guide that we would use with my students when we blog. Looking back on it, I think it's pretty good, but we'll add a few things to improve upon it.
Before we start doing that, we will have to revisit our expectations for leaving a comment. Hopefully they will recall our classroom discussions around leaving comments. We talked a lot about how sometimes our comments are the only way we are known on a blog or on the internet. We need to think about what kind of impression we are making when we leave comments.
Pertinent It should connect to the original post, or original comment.
Positive You want to encourage the author.
Purposeful Only leave a comment when you have something to say.
Professional Use your best writing conventions - capitalization, punctuation, spelling, etc.
In addition to this, I've added another point:
Personal Greet your blogger! "Dear Mr. Arakaki," or "Dear Billy Bob".
My original post drew ideas from Mrs. Yollis' Classroom Blog: How to Compose a Quality Comment.