Off-page optimization is a very important part in SEO, as it is responsible for the organic traffic, which is most important for any website. There are lots of techniques already mentioned above, but many of the techniques considered as spam now a days. Some of them are:
1.Guest Posting
2. Blog Commenting
3. Directory Submissions a they always pending for approval
4. Search Engine Submissions, same as directory Submissions.

Most used and still Effective ways are:
1. Article Submission
2. Local Business Listing if done manually
3. Blog Posting (not comment)
4. Video Posting (Avoid Virool as it is marked as spam site, i read it in this forum)
5. PPT Submission
6. PDF Submissions
7. Infographics (My personal Favorite)

Hope this will help you.