Writing a blog comment needs a sense of well-being, a sense of maturity and responsibility. Thus it should be a "valid" one which could be appealing to the blog's owner/writer and inspiring to the readers/visitors of the said blog as well. Further it would reflect the genuineness and the honesty of the one doing it in which the online advertisers are attracted to it.
There should a need to write the "valid" comment, especially if the blog is to be monetized or make money online, for search engine rank, for a promotion of a certain product or services, among others.
Without your knowledge, the prospective online advertisers or the hosting agency for such ads is browsing them and taking into account, not only the quality of blog, but also the comments left by the readers of that blog.
Most blogs are not in chatting platform. They have form, subject, topic, or product and services for a review. Comments like "napadaan lang", "nice!", "thanks for sharing", among others are practically considered as "empty comments". And outright they should be avoided. They're actually baseless.
For the readers and followers (usually fellow bloggers themselves who are exchanging comments with their blog), if you think you couldn't give a "valid" comment, better skip it and come back later if you've already something in your mind for that blog to write on.
Here are the four things to seriously consider in writing a blog comment:
1. Say something about the title of the blog, especially its relevance and applicability to the content.
2. Say something about the content after reading it. Thus, you may come up with a summary of such blog.
3. Say something about the benefit and its usefulness to the end-user, to the community or even to the country.
4. Relate your personal testimony about the topic or the product being promoted.
Then you've come up with a "valid" comment. By the way, a comment should be a "positive" and inspiring comment for that matter. It shouldn't be humiliating or discouraging. If you couldn't avoid it, do it in a nice way. Tell the truth for the blogger to benefit from it. Do it in a balance way: the advantage and the disadvantage should be in equal footing.
Well, if you're used of making a "valid" comment by taking the four things I've suggested, in so doing, you're already making a review of the content of such blog. And this is one of the influencing factors to increase a blog rank as it is substantiated with a valid review of it.
Be patient and considerate for bloggers are human. They're not robot. That's a valid comment and a review for that matter here in Gil Camporazo's RandomThoughts!.