The broken link building process is used by many digital advertising agencies and SEO experts to build quality do-follow backlinks.
The best part about it? It's Free.
Lucky for your there's no catch; however, you will need to put in some work.
How to begin:
You will begin by searching for broken links on websites in your niche. In most cases, these links are found on the "resource" pages.
Just cruise around on these web pages and look for these links manually or you can use these Google footprints to really get your link search going:
“Your keyword” + inurl:links
“Your keyword” + inurl:resources
When you find a broken link it's best to email the webmaster immediately. This will demonstrate to them you have taken interest in their site.
Here's the catch for them now:
Now that you have provided them with a favor (Notifying/Fixing the 404) ask that they link back to your site in exchange.
There are many webmasters out there who genuinely appreciate this good deed and will do so. This is a numbers game though so don't be discouraged if you get a few no's.