Google Adsense team provided some useful basic SEO tips for higher ranking of your site pages in search engine. Optimizing your site for search engines is long and continuous process. You should take regular steps optimizing your site for better ranking in search engines.
According to Google, the four important points for site SEO are:

• Links
• Design
• Content and
• Structure of site

Links:
Consistently monitor the quality of your sites backlinks. Relevant backlinks from niche sites have higher advantage than the non-relevant backlinks. Also pay special attention to outgoing link. Link to sites, those are helpful to your visitors. Don’t participate in any link schemes. Don’t buy or sell links for getting higher PageRank.
Design and site structure:
Design your site keeping your site users in mind. Keep the site and page structure clear to attract more backlinks.
Create a clear page hierarchy and relevant backlinks for your internal pages. To know more about keywords searched on your site and backlinks to your site use Google Webmaster tools. Create sitemap and submit it to Google. Title tags <title> are very useful for ranking pages for particular keyword or key phrase. Describe your site images using ALT attribute.
Content:
Add original and organic content regularly to your site. This will help to attract more backlinks and Google crawler will also crawl your pages frequently.