Ken Lyons wrote a very good article on Search Engine Watch about taking steps to fix your
website. For those that have not been hit by Panda yet, Lyons pointed out that the Panda will eventually take down sites that it feels are not in line with Google guidelines.
He points out how to take care of duplicate content and prevent it from further happening and gets into what low quality content is and how to beef it up or remove it.
The article is a good one to bookmark and refer back to especially for webmasters new to the game who don't have the budget for hiring an SEO firm.
Read the article on SearchEngineWatch.com