Using your favorite search engine to do a Web search for "Joomla! SEO" will help you on your way when you want to know more about optimization techniques. You might also want to have a look at these sites:
A tutorial on Joomla! SEO: www.compassdesigns.net/joomla-blog/top-10-joomla-seo-tips-for-google.
Joomla! SEO blogs: http://seo4joomla.wordpress.com, www.alledia.com.
Browse the SEO and Metadata and SEF categories of the Joomla extensions directory (http://extensions.joomla.org/extensions) to get an idea of the many extensions available to assist you on optimizing your sites search engine visibility.
There's an exhaustive book on Joomla! 1.5 SEO by Herbert Jan van Dinther available: see http://www.packtpub.com/joomla-1-5-search-engine-optimization-seo/book.