Comments are a very important part of blogging. According to this Public Relations Matters blog, active blog commenting is important because it creates community between bloggers. This only makes sense, since blogging is similar in a social networking site in that you can subscribe to your friend’s blog posts or just any blog you find interesting. On some blog sites like Tumblr, you can even re-blog blog posts that you like to your own followers, without having any worries about copyrighted information.
Another way to create community using comments, is to comment on blogs of writers, organizations, or companies that don’t know you personally to become associated with them in some way. For instance, you might make a series of interesting and professional comments on a blog such as PR Daily and catch one of their blog developers’ eye. This could lead to you getting offers to write a few posts on the blog, and before you know it, you could have a job! Also, it’s a great way to share your thoughts with like-minded writers.
To leave an effective blog comment, I would suggest that you focus on making your comment memorable. Whether you are leaving a comment that puts the blog post in a positive light, or a comment that puts the blog post in a negative light, you want the writer to be struck by your comment in order for them to respond.
However, I would also caution you to never leave any malicious comments on another blog. You have to be sure that everything you write, especially when posting negative feelings towards a blog post, must be one-hundred percent factual. That is, of course, unless it is something that can not be proven false.