The default 404 error page is displayed by the server, but it is not clear enough for novice Internet users. It does not provide an explanation of why the error occurred, nor does it provide any means to get back to the page. They are dead ends that can frustrate users and drive them away from the site. The solution to the problem is to create a customized error page that provides a clearer explanation of the problem and provides a solution to get the visitor back on track. To trigger the display of a custom error page, simply modify the .htaccess file to tell the Apache server what to do when a URL doesn't work.
Find bad links
Providing helpful 404 pages is great, but even better is locating and fixing bad links so users don’t have to deal with 404 errors at all. Webmasters can use Google Webmaster Tools to view specific pages with 404 error links in the background.
Elements of a successful 404 page
In addition to knowing how to trigger a customized 404 page, it is more important to know how to design a 404 page. A well-designed 404 page should help users recover from errors or bad links without using technical jargon or pointing to information that accuses users of ignorant navigation choices. This is a great opportunity to turn a frustrating user experience into a positive one and increase the time users spend on your site. For best results, remember these simple guidelines:
The design should be consistent with the rest of the website.
Include clear information that acknowledges the problem, explains possible causes (don't blame the user), and offers a solution.
Avoid technical jargon. Many users may not know what a 404 error means.
Includes a search box so users can find what they are looking for.
Include a link to the homepage.
Include a link to the sitemap, which provides links to all major sections of the website.
Includes an option to report broken links (contact links).
Optional: Suggest popular destinations on the site.
Never automatically redirect users to another page, such as the home page, as users will not know an error has occurred and will be confused by what is happening.
The design of the 404 page does not need to be too serious. On the contrary, some cute, lively, and humorous elements should be added to the 404 page.