Google regularly update their algorithm to reduce spam activity and fetch quality content and give the more relevant result. Google recently update their algorithms on 24th April 2012 which is called google penguin. Google penguin work on de ranking website which used unethical SEO techniques or break search engine criteria. If your site is one of those hit by penguin, following activity helps to save from Google penguin update.
• Do not use keyword stuffing
• Upload Quality, unique and relevant Content
• Natural link from quality website
• Never violet search engine criteria ( Follow search engine rules)