What, in your opinion, are the three most important tips for marketers to implement with regards to SEO?

What, in your opinion, are the three most important tips for marketers to implement with regards to SEO? That is, if you were a SEO consultant for a small business owner, what three tips would you insist that the entrepreneur immediately change on his website?

Be sure to give justification/rationale for each of your opinions. For example when you state your first tip, explain why you believe that it must be fixed by the small business owner to aid the ranking of his website.