Don’t reply to the SEO spam you get via e-mail
Don’t wait too long to implement SEO
Don’t take your decision to hire an SEO company too lightly
Don’t hire an SEO company and then divorce yourself from the process
Don’t spread your content over several domains
Don’t waste your time submitting your URL to search engines
Don’t make your web site uncrawlable
Don’t target overly general keywords
Don’t stuff keywords in your meta tags, image alt tags, etc
Don’t allow both
www.yourdomain.com and domain.com to resolve to your home page
Don’t ignore usability
Don’t give up on creating great content because you think your customers don’t need or want it, or because your product or service doesn’t lend itself to great content
Don’t develop an unbalanced link profile
Don’t request the same exact anchor text on all links to your site
Don’t plaster your link all over blog comments, guestbooks, etc
Don’t fret over keyword density
Don’t obsess over Google PageRank
Don’t check your rankings every day