While Google Webmaster Tools does show I am getting 404 errors on my site, they are all due to the the lower quality guest author posts that I recently deleted. A spot check of the errors didn’t turn up any external links to these pages. So because a 404 is not a frequent occurrence for my site, it’s not a top priority (hence my upfront criteria that I didn’t want to spend a lot of time on this task). Nevertheless I wanted to make my 404 page more useful to my visitor and not a dead end.
Here’s how I added a search box and a list of categories to my 404 page. Now keep in mind that to follow along, I’m assuming you know how to copy and update files on your server and that you are comfortable editing php code.
Let’s say you are a foodie blogger and just posted a recipe on tomato soup. So you wrack your brains – gee what are all the keywords that describe this post? And you come up with “tomato soup”, “healthy eating”, “warm foods”, “easy recipes”. The way WordPress works is (as long as your theme shows tags), those tags will appear as clickable links that will take you to an archive page that show a list of posts that have the same tag. The problem is that unless you have written several posts on “tomato soups” – the tag archive page will just show your one post. Not only is that not useful to your site visitor, but could be diluting your content in the search engine index.
In my quest to make my category pages index worthy, last week I added 
