What are the best SEO off page techniques to do for backlinks?

You can do regular postings on social networking sites.

By writing a blog for your website, your visitors will get a sound reason to keep returning to your site. So, make sure you post a relevant content in the blog section of the website.

Through Blog Commenting you get a backlink from that particular website. So, Make sure relevant comment should be posted on relevant website.

Social Bookmarking is another way to get the quality links for your website.
Directory Submission is one of the great way to earn links.

Creating Shareable Content. ...
Influencer Outreach. ...
Contribute as Guest Author. ...
Social Media Engagement. ...
Social Bookmarking Sites. ...
Forum Submission. ...
Blog Directory Submission. ...
Article Submission.

The different off page techniques for building good backlinks are:

Guest posting
Article submission
Press release submission
Social bookmarks
Classified ads
Infographics submission
Social media optimization

These are the Off page activities which get good backlinks

Social Bookmarking
Document Sharing
Photo Sharing
Infographic Sharing
Video Sharing
Question Answers
Blog Commenting
Forum Posting
Guest Posting