I don't want to spend a few hours giving you lessons on SEO but here are some basics to focus on:
-Do keyword research. You need to make sure that you figure out what keywords you WANT to be found under.
-After doing the research, you need to write down all the keywords you think you want and then label them as a priority and find out how difficult each one will be to break into. There is no guarantee that you can break into any keyword or phrase but I personally can break into first page of google for most keywords or phrases under 20 million results.
-You want a mixture of longtail, midtail, and shorttail keywords. Longtail are 4 to 5 words (sometimes 3), midtail are 2 to 3, and shorttail are generally 1 but sometimes 2.
-Install a good plugin that'll allow you to setup individual meta keywords, descriptions, etc... for menu links. Currently Joomla doesn't support this, you need a third party extension.
-Turn on SEF URLs and Mod_rewrite.
-Make sure you have a 404 setup properly.
-Get your 301's done.
-CONTENT IS KING, start writing content with your various keywords and phrases spread throughout, but do NOT spam them. Use them only when necessary.
-LINKING IS QUEEN, you need both an internal and external linking structure. A good way to build link is to pay someone to submit your website to 500 directories that have a PR5 of higher. I'd also get someone to submit you to various socialbookmarking websites too.
-After you have your internal linking structure setup, develop a sitemap. Submit that to google and any other search engine that accepts them.
-Setup a blog at either BLOG.domain.com or domain.com/blog
-Get yourself submitted to the dmoz directory.
This is all I am going to give you. It should take you awhile to implement what I said above. If you do as I said you WILL see an improvement in rankings.