Commenting on blogs and posting on forums are two good ways to get backlinks to your website, but you need to be careful to adhere to the proper etiquette and never overuse this technique. If you start spamming blogs and forums with worthless comments, it won't get you anywhere because most of these sites are moderated and your comment will be deleted, along with your link.
Blog commenting is a popular strategy for link building, but there is some debate in the SEO community about whether links from nofollow blogs are counted or not. If you want to be sure that your link carries weight, then you need to find dofollow blogs for blog commenting. The easiest way to do this is to look for telltale footprints that are frequently found on dofollow blogs.
An example of this is the U Comment I Follow logo. Website owners who display this image on their site are making it known that they have modified their sites to use dofollow links...