i will explain you about Google panda and penguin update in straight point your post should be natural not keyword stuffing (not too many keywords in your posts). your link should not coming from only one source of sites like if your all links come from forums it looks suspicious in the eyes of Google, now your all links should be come from different sources of sites or it should be a mixture of sites link like web 2.0, articles sites, social-bookmarking sites, edu sites, directory submission, rss, blog comments, video sites, social sites like Facebook, twitter, tumbler etc you can search on google about link diversity, it is very helpful in ranking in google. no duplicate content if you submit your same article to multiple sites it is duplicate content google takes it seriously now due to penguin update. No blackhat automation seo tools which build thousands of backlinks in hours and if google find any blackhat activities it will punish very badly. your link building process should be natural. if your sites posts have social votes like Facebook likes and Facebook comments the chances of your site ranking will be much higher. do above the steps and you are safe with google panda or penguin whatever updates i don't care because i am not following blackhat techniques fortunately i have learn the white seo course therefore i have never face any problem.
Usually they are announced by Google, to not create exaggerated panic. Read Google Webmaster Blog (they have RSS feeds).
Follow the best search engine & marketing blogs like searchengineland, seomoz . These helps you to know about the Google Panda & Penguin Updates.
Look at the day you lost a significant amount of traffic and check to see what update occurred on that day. That's usually a pretty good indicator.