All the SEO in the world will come to nought if you don't make sure your site takes visitors by the hand and gives them what they want.
Good design and proven usability are just as important as getting a good search engine placement. In short build a great site that users can use and tweak it till you get it right.
Take our site for example. Because of our breadth of offerings our site was becoming complex and confusing. We looked at our analytics and realised we have two types of visitors. Those looking for web development information and Joomla templates and those looking for SEO information. So we simplified our homepage to reflect this.
Look after those hard won visitors and reap the rewards of your SEO efforts.