You most be create a good comments from high PR forums and blogs... and finally you got backlinks.. good luck !!!
While commenting on any such blogs or forums make sure whether the post is not dead that is some time it happens that if you comment on post dated year back will not approve as in this case those comments may be neglected by blog owners as he may not be interested in those comment on topic year back. So try to comment on post which is posted recently. Huge chances of comment getting it approved if some sensible comment has been posted.
For promotion your website, forum posting is the better method to increase page rank concerning website.