In my point of view blog commenting, article submission, forum posting, guest post and press release
on high PR site is the good way of link building and also use social media sites for link building.
Write and create unique and fresh articles, do social bookmarking, article marketing, blogging, blog commenting, guest posting, forum posting, yahoo answers, directory submission, video creation and use social media.
You shouldn't ignore internal linking it is the best method of doing SEO today but apart from internal linking you can post articles on top and high pr article directories this would also give you good and quality link.
There are many free methods which you can use for link building as you are doing link building yourself so you would be learning too and you would be building quality links too.
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