404-link fixing is hardly the newest link building strategy on the block. Web owners use this method to find out whether there are interesting (i.e. high authority) websites linking to non-existent URLs and offering alternate content they can link to instead.
The first step is to look at inbound or outbound links from sites that have like content. There are many tools to study this, and give reports on 404,301 or 200 error codes. You would then generate a list of all pages/sites that link to a 404 page and find out from the site whether you can offer alternative information to replace the original. Where you don’t have the content, you can update your site with the relevant content before inviting their input.
Creating alternative information
Links don’t need updating if they are within old news pieces. Where your content is very much like the missing content, the webmaster can change the link without having to find an alternative. If your information is more recent, that webmaster may even be open to replacing links that are still working.
Ensure that your content has the same tone/gist as the missing content so that the text surrounding the link on the directing page doesn’t have to be changed. If you’re too lazy, you can get a cached copy and rewrite the original piece (to avoid copyright infringement) before asking for a link back to you.
Contacting the webmasters
Use semi-formal but respectful language, since you’re asking for a favour. You can say something along the lines of:
“I was going through <enter URL> and noticed that <enter missing link/text>no longer offers information on <subject/topic>. I ran some searches and found <enter URL> that you could link to which addresses that subject/question. You can simply update it to your page”
You can even send this message to a website owner, it would still work. 404 fixing has a high success rate in terms of link building. Over 60% of contact emails raised for 404 fixing can lead to a back link. Exceptions only arise in cases where a webmaster does not wish to update certain information.