Utilise Broken Links
Its a fact that people make mistakes. Anyone who pays attention to web analytics will no all about 404 errors and broken links.
Broken Links
Just look through your web stats or Google Webmaster tools and you will no doubt see some links to pages that don't exists on your site. Normally these are just dead and broken links but there is a way to make these work for you.
Usually it is obvious where a link was meant to go, common causes are miss spellings or a keyboard entry. Thats why you should always check your links right after you write them.
Where someone has made a mistake with a bad link, create the page with some relevant content and then 301 redirect it to the page it was meant to be. Hey presto you now have link weight coming into your site and filtering through to the relevant pages that would have otherwise gone completely unrewarded.
The SEO Files Recomends
Make your dead and broken links work for you by 301 redirecting them to the relevant pages.