One of the worst things that can happen to your business is someone spreading a link to your site that is broken, it will frustrate anyone who followed it and negatively impact your SEO (maybe, its a guess). Some savvy web developers have been using custom error pages for quite some time and this is my personal approach to creating a error page.

404 Error pages should do three four things;

Alert the visitor that the page cannot be found.

Suggest pages that he may be looking for.

Notify the webmaster of the broken link so he can add a 301 Redirect.

Provide a "Call to action" so the visitor doesn't leave.