Many consider flash a bane to optimizing for search engines. However, there are some things to do to improve visibility.
The Steps.
1. Title, keywords, description and keyword density need to be researched.
Determine the combination of terms people use to find your site. Consider how many keywords are used, target descriptions, appropriate titles, and the frequency the words are used (look at competitors to get an idea).
2. Spend most of your time getting good sites to link to yours.
Do a search using the keywords you researched in step 1. Try contacting webmasters, requesting a link, to those you think are receptive. If emailing is not your thing, build a reputation in appropriate forums or groups. Sometimes it is better to be known first, before contacting someone for a link request.
Another place, to find good sites for linking, is trade associations, public organizations, and complementary sites. Complementary sites have the bonus of linking power and relevancy to your site.
Conclusion.
A 100% Flash site, following these steps, gets good results.