It includes forum posting, blog commenting,
These activities, if used for the purpose of promoting your site, will not help.
Any reputable forum or blog will mark external links as "nofollow", so they will not help you rank on search engines. You also run the risk of falling foul of Google's guidelines on link schemes, and having your site penalised as a result.
Additionally, creating links that weren’t editorially placed or vouched for by the site’s owner on a page, otherwise known as unnatural links, can be considered a violation of our guidelines.
And, of course, you risk having your comments deleted and possibly being banned from the site.
If you are commenting or posting with the intention of adding something interesting to a discussion, then people reading your contributions may be interested in learning more about you and follow your links, thus bringing you some traffic. But this relies on high-quality posts, not posts clearly made for promotional purposes.