Broken link building is the art of finding useful resource or favourite link sections of a third party site that is relevant to your niche and then seeing if any of the sites mentioned no longer work. A lot of these suggested sites or resources have been around for a while and the keeping the list up to date can be quite the task for the webmaster. You basically find the broken links and let the site owner know that they have links that no longer work and offer your site as an alternative.
Another way to find them is to use specialised software that will find these kind of links for you. One of my favourite is by Citation Labs http://www.brokenlinkbuilding.com/ This tool seems expensive at $67 a month but the kind of authority domains you can find is well worth the investment. You basically add keywords for instance “business training, “business development”, “business coaching” and it will find sites that list resource or link pages.
Another way is to use tools to reverse engineer what your competitors are up to. Again this is more fruitful for the niches above. Sites we recommend are:-