In short, commenting will not help you. It may drive a few hits here and there to your site, but search engines will not consider those links as authoritative links.
If you comment on dofollow blog , then search engine will consider as authoritative links. You can find lot of dofollow blogs on internet using normal search engines or special dofollow blog finding software.
Commenting on blogs is a great way to receive traffic.If you are just using it to post a link and not adding value to the conversation, few people will likely let you comment, or won't approve them. So,be sure you give a good commnet.