Basically you should optimize your videos for YouTube as well as you are optimizing your pages for search engines, just with a little shift in rankings factors. The most crucial thing here would be to create descriptive titles and great comprehensive descriptions optimized for your keywords; Google will make use of it to determine the relevancy of your videos as it cannot actually watch them. You should also build some links to your videos from relevant websites, share it across social networks and use blogs/forums to spread the word.
You may also think of targeting the 'video' keywords from the beginning - these are keywords that are more likely to return the videos among 'universal search' results; this will enable you to rank in the 'universal search' apart from ranking in 'video' tab, which is cool. There are tools that allow you to check if your potential keywords return any videos, and to monitor the rankings of your videos later - in Google or in YouTube search directly.