Unless you've been living under a rock for the past 4 years, you know how popular and widely used Facebook is today.

Just a couple of years ago, you had to relentlessly encourage family and friends to join this social networking website (shortly after others had convinced you to join). Nowadays, it's rare to find someone who hasn't got a Facebook account.

Here are 15 important website design tips that you might not be aware of or have overlooked. Consider taking advantage of them if you haven't already done so...

1. Custom 404 Pages

Create a custom 404 web page, so that any time your website visitor mistypes or misspells a URL on your site, they will still be provided with navigation options for your site (instead of getting nothing but a "Page Not Found" error message, which is neither friendly or helpful).