sh404SEF, AceSEF, JoomSEF are the best SEO Extensions for Joomla.. But of these three i prefer sh404SEF extension.
download this extensions to your website configure and enable them XMAPS module this is the best sitemap generator extension currently available on joomla extension directory it even index your images and generate google news sitemap for your site which will icrese you site google page rank and create easy access for google bot on your Simple Related Article Module this module will link your joomla articles to each other by using your keywords, this will let your pages link to each other which will enable visitors to navigate to each of your article from one to another, and will help in icreasing your website pagerank on search engines. Mobile joomla extension this extension will generate a mobile site for your pages and will arrange your contents properly it is good because this component has an iphone page, smartphone page and imode page you can even put adsense code to your mobile page to earn more from your visitors