Find some resources in your industry/niche
See the top 20 of them and check them by number of backlinks pointing to it.
Make a valuable resource on your website that's better than all of those already there and then reach out to as many of the sites linking to your competitor's resources.
However, this won't work if your site is new or less than a certain DR. Sites with high DR won't want to link to a lower DR site in many cases, so you'd need to focus on those in the same range and lower (and not your direct competition).
Might help if you offer them a freebie first