Here are a few general ones:

  - Join forums related to your site and post about it
  - Write guest posts on news or blogging platforms that point back to your site
  - Ask other people to share links to your site on social media, their own websites, whatever
  - Sponsor sites, podcasts, or videos so they include links to your site on their pages

What kind of site are you trying to promote?

Edit: Formatting

I remember that Simpsons episode when Homer creates a website, which contained nothing controversial, and full of bells and whistles, yet thin on content. Then he wrote an article about something controversial, and his visitor numbers went through the roof.

This is content marketing 101. Discover something new, tell people about it, profit. The backlinks will happen naturally and organically. You may even have your article featured in some high profile website that gets 10,000x more traffic than your site, boosting your SEO in the process.

Create interesting content.

Create good content is important, but if no one's ever gonna read it then it's not gonna give you any backlinks.

It goes both ways.

The average content marketer is lazy, wants to write one article and have it get zillions of views.

The average content marketer writes spammy articles that exactly zero people are interested in and wonders why it is so impossible to get backlinks.

If that content marketer created articles that people were interested in they could prime the pump on social media or with paid advertising and it would create a chain reaction of getting more links... (e.g. "going viral")

The average content marketer however can't do that because they are 100% self-centered and can't even imagine what other people would find interesting.