SEO Rules & Best Practices

We've search far and wide on the internet and compliled this list of SEO best practices. This list is not comprehensive but tries to be - it's a rapidly changing area.

Definitions

Search Placement.com has a good glossary of SEO terms as does this business geek.

Content Concerns

Are the keywords you're targeting relevant to site content: Ensure that all content on the site is targeted towards the core message of the site, for example there are no pages here related to sports or entertainment.
Are targeted keywords popular phrases used in search engine queries?: This
Accurate, Focused & Unique Page Title: The title is one of the most important attributes of the page
Accurate, Focused & Unique Meta Description: The meta "description" increases relevance for the page and is also used in search result clips, summarize the content and make sure this description is as unique as the title
Use H1 elements for prominent content titles: Certian elements, like H1, H2 and H3, are weighted heavily by SECAR

Usability Concerns

Create Custom Error Pages: Create custom pages for 404, 410 and 500 level error messages. Use it to point users in the right direction - hopefully SECAR will not see this. Use Webmaster Tools/Log Analysis to monitor.
Use Intelligent Redirects: When pages move on your site use a 301 Permanant Redirect.
AVOID pop-ups
: for ads or anything unless absolutely necessary e.g. Help or Survey type pages

Structure Concerns

Use URLs that are simple and look static: URLs should look like simple pages, reduce the number of Query String variables to two maximum.
Use keword relevant directory and file names: The SECAR are sensitive to these paths in your domain. Use relevant/targed words. e.g. /services/consulting vs /static/service1.html. Even database driven sites can have paths like /products.asp?brand=12&category=&37,45,12&sort=-4 rewritten to /products/acme/rockets,skates,tnt/by-price.
AVOID Flat URL structures: Some sites make all pages under the root, use a clearly defined heirarchy for pages. e.g. /services/consulting/seo vs /services-consulting-seo.
AVOID spamming-sih file names: Use sane names e.g. /products/brand/acme vs /products-acme-tools-rockets-catch-roadrunner or worse /products-tickets-superbowl-tickets-football-nfl-tickets.

Inbound/Outbound Linking

Your relevance to many of the search engines is based on how many sites link to you. The more high quality links pointing to you the better.

Link Quality: The relevancy and page rank of the page point to you. Ideally it's pages of related content matter with relativly high rank themselves. A PR 5/10 page about Shampoo pointing to your page at /products/shampoo is valuable. A PR 9/10 page about Beer Pong not not so much.
Build Links through Blogging: Search engines love blogs, especially when hosted on a commercial provider like blogger.com. Use these to announce your site and create short intelligent keyword rich entries with links to your main sites relevant pages.
Link Out to Relevant Content: Search the web and find some further back information and link to it. Adding value to other's pages is a good way to build relevancy for a topic.
AVOID Link Spamming: AVOID paid services, AVOID thousands of low value links (aka: free-for-all linking). Use a designated channel for advertising and alerting the masses such as a blog or PR service. Organic link building takes time but builds a more resilient link foundation.