Common SEO mistakes include using keywords excessively in titles, having high keyword densities, lacking an XML sitemap, not including keywords in URLs or using unique meta data and descriptions for each page. Other mistakes are overusing H1 tags, using the same anchor text for all links, not setting up 301 redirects, lacking keywords in content, focusing too much on meta tags, not providing HTML alternatives to Flash sites, engaging in keyword spamming, choosing a crawler-unfriendly CMS, and not promoting the site.

2. High keyword densities.

3. Not having a Valid XML Sitemap.

4. URL’s not containing any keywords.

5. Using H1 tags more than once on a single page.

6. Not giving each page unique Meta data.

7. Using the same anchor text in all links.

8. Putting analytics code at the beginning of your body content.

9. Not using accurate image descriptions.

10. Not having a 301 redirect setup.

11. Lack of keywords in the content.

12. Concentrating too much on Meta tags.

13. A Flash Website without a HTML alternative.

14. Keyword Spamming and Stuffing.

15. Picking a Poor Content Management System.

16. Use Crawler Unfriendly Development Methods.

17. Not Investing in Site Promotion.