Dofollow backlinks are hard to get, in other words it should be earned. You cannot just simply link to any site. Because a link is considered a good link if it comes from a high quality, reputable and relevant niche sites, regardless if it is nofollow or dofollow.
Off Page SEO techniques help to get more dofollow backlinks...
1. Forum Postings
2. Social Bookmarking
3. Directory Submissions
4. Blog Creation and Blog COmmenting
5. Guest Posting
6. Article Submissions...etc
First you search High PA DA Sites regards your website.
Like as a Relevancy, Authority, and Uniqueness Sites For your site.
If you try above points for your site surly you will get benefits for your website.