Blog comments are what make a blog interactive and social. The most popular blogs have a very interactive community who voice their opinions on posts frequently. It's that social aspect that makes blogs such a powerful component of the social web.
Give comments base on your ideas, thoughts and knowledge about the topics that is relevant to others. Avoid filler words and spam.
Spammy irrelevant comments are likely to be ignored and removed/unapproved. Put some effort into comments, relate them to the post with specific references to post content.
This is also a problem with me. When I see a long articles then I always try to read atleast first & last paragraph and other comments other wise I do not comment there.