1.First of all read the blog content care fully and after then post the comment on the blog.
2.Always start with the writer name.If you address the writer you will make your comment more personal.
3.You should post at least 3 or 4 sentences.Be careful we are adding value to the original post.
4.Try to be different, controversial, and crazy.
5.Relevancy is very significance part in blog commenting so post comment in relevant blog.
6.Add the comment that add the quality of discussion.Do not use gimpy commenting like "nice post, i enjoyed your post etc.
7.Avatar is also the important thing for blog commenting.This avatar is simply an image this is displayed along with your comment.The plain and default avatar with comment screams either comments spam.you can register here at gravatar .com.
8.Reply to first commenter.
9.Leave long comment.
Bonus tips:Here is a strategy that is sure your post will get indexed very fast.After leaving relevant comment you can conclude with something like this"I enjoyed your post so much i am going to bookmark it for you.