if you want quality based backlinks then try Article Posting, Blogging and you already doing Forum Posting.

build natural backlinks

You have to do Off-page SEO activities for building the quality backlinks for a website. SEO activities such as forums posting, guest posting, article submission, blog posting and business listing submission are really effective for this kind of work.

We can create backlinks using off-page submission. More backlinks come in forum submit.

You can build back link by off-page activity, like

1.Directory Submission
2.Social Book Marking
3.Article Submission
4.Forum Posting
5.Blog posting

Backlinks, also known as incoming links, inbound links, inlinks, and inward links, are incoming links to a website or web page. In basic link terminology, a backlink is any link received by a web node (web page, directory, website, or top level domain) from another web node.

to give backlink use forum posting article/blog posting blog commenting press realse directory submission.............

To create the back links to your site, link building techniques are used.

create links easily. write words that will last you a link just click the link

To create good backlinks for your website use following techniques:
You can use various social networking sites like Facebook, google plus, twitter, Linkedin etc.....
You can also use search engine optimization techniques as forum posts, social bookmarking, image backlinking etc......

best option is great content which is share by others ( takes time and effort )
good quality directories
comments on forums
comments on blogs
quest posting
also profile on Google+ counts ( in your profile set up your website ). Similar with Facebook
very good backlinks comes from YouTube - make a movie and in description add link to your website