Gary Beal, also known as GaryTheScubaGuy to our regular SEO Chat forum readers and members, came out with plenty of great SEO tips for 2007. Since he has expanded, updated, and revised this list, we've been presenting them in sections to help you have a banner year in 2007 and 2008. This is the fourth part of the series.
7. Run Regular Monthly Basic SEO Checks
This is a list of basic SEO tasks that should be the first thing that you check on all of your pages. Many times I find myself looking for the more technical issues, only to find out from one of our freshman SEMs that there was a 302 redirect rather than a 301, or worse, there was a doorway page or hidden text from a previous SEO company. So I'm including this list as a checklist for you to use.
The search engines look at traffic in their algorithms to "grade" a page. If you have a complicated URL, one that is commonly misspelled, or do something else that could cause you to lose any existing links that are published out on the web, this is the landing page the visitor will get sent to. If it has your template and navigation from the rest of the site it will get indexed like a normal page. Change your title and meta tag to one of your keyword strings, add an image and relevant content that reflects your keywords as well. I avoid placing the actual term "404" on the page.
Some of the ways 404 pages are reached are:
Bookmarked sites that have since been moved.
The end-user made an error when typing in a URL.
A moved page is still indexed in the SERPs.
There are broken links in your link structure
What are some tips when customizing your 404 error pages?
Put a link to your FAQ page.
Put a link to your top level categories.
Put a link to your sitemap.
Create a template 404 page that blends with your site.
Add a search box.
Make your 404 pages look as close to your site theme as possible.
Add true navigation to it.
Optimize this page with the same elements as your other pages.
A simple statement like "You have found this page in error, please select from the menu on the left side of this page" will do here, and you will retain more traffic.
Search Optimization 
