Building backlinks is super complicated task nowadays but below are the strategies that my team has been working with for our clients and they have benefited from the work:
1) Make relevant guest contributions - A lot of high authority blogs have changed their guest contribution policies and made the links no-follow but there are still websites out there that give do-follow links. So, discovering blogs that are relevant for you and pitching a post that actually adds value to the blog can get you a quality backlink as well as exposure to an engaged audience.
2) Pay for feature posts - Media sites accept features posts and give do-follow links in them. Usually expensive but think of long term and put in some money on it from time to time
3) Associate with NGOs - Reputed NGOs are always interested in people who can support their cause and most feature their supporters on their websites. Links are often given to websites on such occasions.
4) Get active on relevant channels - There are no dearth of content creation, content curation, business listing, and community websites. Such websites usually have authority and backlinks from them can be counted into decent quality. So, get on all such websites and participate from time to time as well.
5) Last but not the least, create authority content. Authority content is picked up and referenced on its own which creates automatic backlinks. When I say content, think blogs, images, infographics, and everything else that can be credited/published with a link.
There are many other ways to create quality backlinks. Please reach out in case of further help!