The user experience starts on the search engines
When searching, people visit multiple sites and will frequently do several searches until they find what they want. Visitors may have looked at competing websites before seeing the client’s site, and they very likely will enter the site on a subpage. Make it easy for these prospects to find their way.

SEO is about increasing conversions
SEO done properly should attract more people to the site who are as close to purchase as possible. Every page is a possible point-of-entry, although the top level pages are more likely to be entry pages. Therefore, the site needs to support quick conversions. This may mean putting the contact information on every page, or it could be a call to action on every product page. Installing Google Analytics at launch will help your clients monitor their traffic and conversions.

Pages must be crawl-able and parse-able.
A spider must be able to move through the site, and it must be able to read all content. Spiders cannot access content that is in Flash (unless the .swf is specifically created to be read by spiders) or content that only displays using javascript or AJAX. Spiders cannot read text that is in image format, unless the text is put in the alt attribute of the image tag.  Make sure you don’t use secure servers unless you have to, as spiders often have trouble crawling these pages.  Also, have a crawlable HTML site map on the site, an XML site map registered with Google and Yahoo, and a robot.txt file.

You may already hate SEO
Designers don’t like pages with lots of copy, but SEO depends on having lots of keyword-rich copy. If you design the page to scroll, you can have a airy, open look at the top of the page, and push the text lower. Headlines need to be HTML text using H tags, not graphics, and the nav should be text (you can use graphics if necessary).  Create HTML text links in the copy using important keywords.  In order to keep text prominent on pages, move all javascript and styles to external files.  Note that many of these rules not only help with SEO, they are also needed for dynamic sites. For example, a site built in Joomla, Drupal or any other CMS should use text for the navigation rather than images.

Use unique tags
Each page will need a unique title tag and meta description tag, and the alt attribute should be used for important images.  While the keyword tag is less important, it should still be utilized.

Avoid tricks
The spiders need to see the same content that the humans see. It’s easy to use styles to hide ‘SEO-ified’ content. This can get your client’s site banned from the engines. If you must display content that only humans can see, such as content displayed using AJAX, make sure you provide an alternate means to access the content.

Websites need to be updated regularly
A page that is updated regularly is more likely to have relevant and current information than a page that has not been updated for years. Search engines consider this when determining a page’s rank. Clients should have the ability to update this information, either through a CMS or by having a maintenance agreement with you.