SEO is an ongoing process. You need to keep up with your site to remain on top of the search results. One of the main jobs is to find the pages on your site that return errors. Find those pages with broken links and correct them.You should also get rid of duplicate info on your site. That means duplicated across your site, and duplicated by others. Make sure your pages are relevant to your site's keywords. A quick way to do that is to put tag clouds on all your pages. Then you can see if they are relevant.
Good luck.
