Matt McGee of Search Engine Land gives us 21 essential SEO tips and techniques to yield improved search engine rankings. Here are the DO's:

1. Commit yourself to the process.
2. Be patient.
3. Ask a lot of questions when hiring an SEO company.
4. Become a student of SEO.
5. Have web analytics in place at the start.
6. Build a great web site.
7. Include a site map page.
8. Make SEO-friendly URLs.
9. Do keyword research at the start of the project.
10. Open up a PPC account. Whether it's Google's AdWords or Yahoo's Search Marketing or something else, this is a great way to get actual search volume for your keywords.
11. Use a unique and relevant title and meta description on every page.
12. Write for users first.
13. Create great, unique content.
14. Use your keywords as anchor text when linking internally.
15. Build links intelligently.
16. Use press releases wisely.
17. Start a blog and participate with other related blogs.
18. Use social media marketing wisely.
19. Take advantage of local search opportunities.
20. Take advantage of the tools the search engines give you.
21. Diversify your traffic sources.

Now that you know them all, you can do your part.