Google's Matt Cutts presents suggestions and resources which may help address a sudden, mysterious drop in your website organic search engine rankings. Anyone concerned about poor search engine result pages (SERPs) should watch this video for an overview of possible fixes and remedies. "What steps can I take to diagnose a drop in ranking?" is worth viewing even if your websites do not (presently) have organic search problems.
Matt Cutts is Google's Chief Engineer in charge of Google's web search quality regarding spam.
Also view What to expect in SEO in the coming months from Matt Cutts, issued on May 13, 2013.
For additional resources, try the Google Webmasters Resource site for valuable insights and guidance on optimizing a website for Google Search.