Other than making your 404 error page user friendly, you can redirect it to your index pages such as the homepage, sitemap, or search page, to make it useful for the users. Instead of relying on them to correct the error themselves, you offer the new orientation.
How to redirect a 404 error page to the home page?
There are essentially 3 ways to do this depending on the technology your site is built on.
The .htaccess and HTML solution
This works across all sites that are served by the Apache web server with .htaccess enabled. Add this line in the .htaccess file in the root directory of your domain:
ErrorDocument 404 /404.html
And in 404.html, add a meta tag in the HTML head section:
<meta http-equiv="Refresh" content="1; URL=http://www.example.com/">
So when there’s an 404 Not Found error the user would be first redirected to /404.html and in turn, he or she would be redirected to the homepage http://www.example.com/ (or whatever you change it to) by the meta Refresh actions.
The PHP solution
If you are using PHP to code your site, chances are you know this solution. You can always use the previous solution (The .htaccess and HTML solution) to redirect 404 error page to your home page on a PHP site, but you can also try the pure PHP approach instead.
Whenever a user types in a URL request that you do not recognize, render this:
header("HTTP/1.1 404 Not Found"); header("Location: /"); exit();
Which would redirect the user who has hit a 404 error to the homepage / or any other page URL you specify there.
The WordPress solution
If you are using WordPress for your site, make a 404.php file in your theme directory with the following content:
<?php header("HTTP/1.1 301 Moved Permanently"); header("Location: ".get_bloginfo('url')); exit();
WordPress would automatically use 404.php as the default 404 Not Found error page and when a user hits that page, he or she would then be taken to the home page your WordPress blog.