Great (not good) content + Good promotion = Traffic. Once people engage with great content, and thus (organically) share this content, you can bet that someone down the line is going to link to it. This is the best way to earn links, period. This is your foundation. From there, there are probably many Industry websites where you might have an opportunity to list your business or Industry publications in which you might earn an opportunity to write an article (the by-line will often contain a link back to your website).
You can also seek out opportunities where old content earned a ton of links (perhaps a competitor earned many links for a post they had written 5 years ago, and the topic needs to be revisited/refreshed), where you can rewrite the piece/update it and then reach out to the websites which had linked to the (now outdated) old piece. You can also find broken links and reharvest these (perhaps you had a page/post that had earned links, but – for whatever reason – the page is now a 404).
Perhaps you could republish the piece (or update it, if that’s required) and now regain the “lost link”. There are many other “gray hat” opportunities for growing your link profile which include sponsorships of events/charities, and other “darker gray” opportunities which include providing scholarships.