These are the important backlinks for increasing ranking
1.Social Bookmarking
2.Directory Submission
3.Blog Posting
4.Article Submission
5.Blog Commenting

Six Crucial Link Building Strategies for SEO and Traffic
1. Understand Google’s quality criteria
2. Focus on relevance
3. A diversified link-building strategy is a key
4. Don’t follow the same link-building strategy as your competitors
5. Make your anchor texts natural in each link you build
6. Always keep point #1 in mind

The best way to increase backlinks is Commenting. I recommend you to check out all commentluv blogs. To get a list of dofollow blogs, go to Google and Search for dofollow commentluv enabled blogs. Then you get a list. Slowly build links. Never comment on all blogs in one day.

To improve your back-links you most follow below techniques..

Article Submission
Guest Posting
forum Posting
PDF Sharing
PPT Sharing

Off Page is process of getting backlinks to your website-
Profile creation
Image Sharing
guest Posting
PDF Submission
Business listing
Article
Blog.

To improve backlinks you need to be selective while selecting websites from which you expect backlinks. Always go for websites with good page authority and domain authority. Choose a website with alexa ranking less than 200000. Like this forum is good as its alexa ranking is 89,768. Don't just go for getting links from anywhere. Guest posting is the great source of good backlinks.
Thanks

forum posting
directory submission
Social bookmarking
blogs
press release

follow these for quality backlinks
Step 1: Find sites or resources that have changed names, shut down, or moved.
Step 2: Find sites linking to the old page.
Step 3: Give them a heads up about their outdated link.
And you’re set.