Commenting is one of the most popular ways of driving traffic to your own website or articles. However, because of its popularity, when you are commenting, you are competing with other readers for the writer's attention. This is why it is important that your comments have value.
What is value?
The value of a comment is its ability to attract the writer's and other readers' attention enough to convince them that they should check out your own website, blog or articles. Adding value to your comment is highly useful when commenting to blogs with NoFollow links in their comment section. If you can convince your audience to visit your website, that is one step in convincing them to link to your site or one of your articles. Value is also indispensable when commenting on blogs with high amount of traffic. These blogs usually receive a lot of comments and a stronger comments easily overshadow weaker ones in no time.

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How to add value to your comments
1. Be specific
Stop using general words like "great," "nice," etc. If you think an article is great, tell the writer what is great about it.
2. Look out for abused words
Words like "Interesting!" and "Love it!" are some of the most abused comments in the web. Stay away from them.
3. Add a personal signature
You can add a personal signature not only through unique greetings but also through your tone. Your choice of words can be your signature.
4. Oppose when given the opportunity
As long as you can defend your position in a cool manner and with facts to back you up, you should express opposition in your comments. It always gets the writer's attention.
5. Add a relevant fact or idea
Comments with relevant fact or idea becomes part of the article itself which will earn you respect from other readers too.
6. Share an interesting experience
Experiences would make your comment alive. Other readers would also like to read personal life account from a fellow reader.
7. Ask questions
When you have something you don't understand about the article, ask the writer to clarify it for you. It will create a conversaton between you and the writer.