From Grammar Girl:
Rule #1 — Determine Your Motivation
People have different reasons for writing blog comments. What’s yours? Are you trying to get the attention of an influential blogger? Drive traffic to your own blog? Establish yourself as an expert on a topic? Do you appreciate the person’s work and want to say thank you or brighten his or her day? Do you disagree so strongly with what you’re viewing or reading that you simply can’t let it stand without a rebuttal? Sometimes, understanding your motivation will help you decide what kind of comment to write.
Rule #2 — Provide Context
I know as you’re writing your comment *you* know what you’re responding to — maybe it’s the article or video or maybe it’s someone else’s comment, but when people come to the page later and read the comments, it isn’t always immediately clear what you’re talking about. It’s most important to provide context when there are a lot of comments. If comments are coming in really fast, for example, yours can get separated from the comment to which you’re responding.
For example, instead of just starting out “Humidity is important too!” it’s helpful if you start with some context like “User Squiggly1234 has a point about chocolate storage temperature, but has missed one important variable” and then go on to talk about humidity. That way other commenters won’t be confused as to why you started talking about bad hair weather on a post about chocolate.
Rule #3 — Be Respectful
I shouldn’t have to tell you this, but comments that start out “You’re an idiot,” are laced with profanity, or are just plain disrespectful, undermine the authority of your argument. Nobody gives much credence to an obnoxious troll. So aside from the pleasure you get from annoying people, you’re wasting your time writing such comments. Always remember there is a real person reading your comment. It’s easy to be mean while hiding behind the anonymity of the Web, but you shouldn’t say anything you wouldn’t say in person.
Rule #4 — Make a Point
Sure, most bloggers will lap up short comments like “Wonderful!” “I love it!” and “Thank you,” and if all you want to do is express gratitude or brighten their day, comments like that are fine, but you’ll make a more lasting impression and a more meaningful contribution to the conversation if you say a bit more. Why is it wonderful? Why did you love it? It’s even more important to make a point when you disagree. It’s a waste of time to just write “You’re wrong,” or a longer ranting equivalent. Make sure you include the reason you disagree. It’s easier than you think to avoid making a point. Consider the comment “You’re spreading lies by saying the ideal temperature for chocolate storage is 28 degrees. At that temperature, the chocolate will go bad.” Really, all you’ve said is “You’re wrong.” You need to say *why* the temperature is wrong. Say what temperature is better and why. Maybe say where you get your information. Is it based on your experience, the recommendations of the Chocolate Storage Association, or just your own wild guess? Make a point.
Rule #5 — Know What You’re Talking About
When I read comments I’m always amazed by how many people admit (admit!) they have no idea what they’re talking about and then go on to make recommendations, suppositions, or write long rambling analyses based on nothing more than a pure guess. I swear I’ve read comments like “I’ve never worked with chocolate before, but I think 29 degrees would be better than 28 degrees.” That kind of comment is not the way to get positive attention from an influential blogger or establish yourself as an expert. If you have a question the author didn’t answer about why 28 degrees is best, it’s fine to ask; but when you’re commenting about something that’s based in facts, you’re not adding anything useful when you write comments based on your intuition. You’re not under orders to comment on everything you read. Save your time for commenting about things where you can actually say something useful.
Rule #6 — Make One Point per Comment
People have short attention spans, and in my experience attention spans are shorter on the Web and even shorter when people are skimming comments. A comment should be just that — a comment — not a manifesto. If you have something so complex and important to say that you can’t do it in a few short paragraphs, start your own blog. If you have two separate things to say about the video, photo, or blog post, it’s usually better to break it up into two separate comments. Remember, people are often skimming.
Rule #7 — Keep it Short
This is really an extension of Rule 6, make one point, but since it’s possible to go on and on about one point, I thought I’d also remind you to keep your comments short. Again, it’s a comment, not your own blog post.
Rule #8 – Link Carefully
If you’re posting a comment with the hope of driving traffic to your own site, think carefully before you include a link in your comment. Of course you should include your link if the comment box has a place for it, but leaving a link in the body of your comment is a risky thing. Many people think it’s great marketing, but a minority of people think it’s obnoxious and pushy.* If you decide to do it, make sure you’ve written a thoughtful comment that truly contributes to the conversation on the owner’s site, not a useless comment that’s just a transparent excuse to leave your link. It’s also considered more acceptable if your link points to something you wrote that’s relevant to the conversation, not just a link to your general landing page.
Rule #9 — Proofread
I know it’s hard; those boxes in which you write comments can be tiny, and they usually don’t include a spellchecker. But proofreading is important because if you have a lot of typos or misspellings, it undermines your authority. Any troll who disagrees with you can just say, “What do you know about chocolate storage, you can’t even spell ‘their.'” If you have trouble proofreading on the Web, write your comment in a word processor where you can see the whole thing and run it through spellcheck, and then paste it into the comment box.
So that’s it, the nine simple rules for writing a blog comment. Did I miss anything? Leave a comment!