There a number of things that you must do in order to make your website SEO friendly:

• minimal usage of Flash
• don’t use frames
• keyword research
• CSS drop down navigation (optional)
• include researched keywords in title, description meta tags
• include researched keywords in content
• include researched keyword in hyper linked anchor text
• include researched keywords in headings (H1, H2, H3 etc)
• include researched keywords in alt tags (images, videos, etc)
• use CSS (Cascading Style Sheets)
  • faster page loading resulting from the usage of CSS means that search engine spiders can more quickly and more efficiently crawl your website

Thanks to the people at ChromaticSites - From the post "The Official "Successful Website Checklist Challenge" | Web Site Design Blog"