Well to be honest, it's VERY difficult to "optimize" a flash site and do it well that it ranks in Google and any other SEs. That's because Google, while they now have the capability to see contents in a flash site, is still light years behind in flash optimization than your "normal, organic" optimization. You have to conduct more OFF-PAGE optimization (like link building, sitemaps, etc.) than ON-PAGE optimization (what you put inside the contents of the page). BUT, if you must do it, here's some ways you can do it:

1) If you know your SEO/SEM techniques, perform keyword research on your content, market, and industry, and place specific keywords on your meta tags: in your meta description and in your meta keyword in your html file
2) In 70-90 characters or less, implement your keywords on your tag in your html file
3) Have a separate Google sitemap of your site (you can create one at http://sitemapdoc.com), then a) upload the sitemap in your site servers, and b) upload your sitemap file in Google (http://google.com/webmaster/tools)
4) Conduct link building/link exchange programs with sites with relevant content or within same industry than you (this will help relevancy of content for you and also establish page weight)
5) If you have a blog, write quality content that is linkable to your main page as well as to other pages / sites. If you don't have a blog, start one.
--> The blog, after it gets more content and more visitors, will help increase page rank/weight within that site, but not necessarily the whole or the domain. BUT, the more the blog receives and gives quality and relevant content, the easier the domain will receive higher page ranking
6) Watch your links, rankings, and keywords monthly and analyze behavior of users and search robots. This will help you figure out any dips or changes Google makes to your rankings and so you can adjust your keyword research and implementation accordingly

These are just some that you can check. Good luck and let me know if you need more help.

David