WordPress is an excellent CMS for building easily edited and updated websites. It also has a well-structured architecture that performs reasonably well and is mostly well-optimized for search engines. However, depending on your use of WordPress, there are a few tips to keep in mind when building your WordPress website.
Without decent content on a page, getting a page to rank organically is an extremely tough and often fruitless endeavor. Simply stuffing keywords has been proven countless times to cause a page to perform very poorly, and provides no real value to a human who finds your page. The best rule of thumb is to write for people first, and fill their need before considering any SEO implications.