Not only should you make a Customized 404 Page, but you should include a special offer to take advantage of something that is usually annoying to your visitor.

A very easy way is to create a static page, and nominate the page in sh404sef .

... call it something like: 404-Page-Not-Found

Enter a message similar to the following... :

We're sorry, You've reached a page that doesn't exist.

Error 404 - Page Not Found

But wait !

Since you're here we'd like to make your visit worthwhile:

<special offer details and link>
<link to an important article>
<etc>

Now any visits using invalid site addresses will be presented with this page !

You can test it out now using this link