There are two types of Google penalties: manual and algorithmic. Combat these penalties and make your site visible again.
An SEO's playbook on coming back from a Panda, Penguin or Hummingbird penalty.
In ice hockey, getting hit with a penalty earns you a few minutes inside the penalty box, the sports equivalent of a time-out. It is a system that has found its way into the Internet arena, in that violating the rules of the game results in a punishment doled out by search engine referee Google. This time, however, the ref doesn't always let you know what the infraction is-and you can't get out of the penalty box until you fix it.
There are two types of Google penalties: manual and algorithmic. A notification will accompany a manual penalty, so the webmaster will know exactly what has occurred and whether it is just an offending page or the entire website; an algorithmic penalty will receive no such notification and requires a little investigation as to its cause (Tweet This!)
Algorithmic penalties are an unfortunate consequence to changes in Google's search algorithm, which is frequently updated and tweaked (as in, hundreds of times per year). Major updates usually receive codenames and a flurry of attention, like the recent Hummingbird update that overhauled the algorithm. Other times, the updates are minor and get no fanfare.
Hummingbird, announced on Sept. 26, 2013 (Google's 15th birthday) but launched a month earlier, is the largest of all recent updates. The new algorithm was said to make it easier to "have a 'conversation' with Google" and focuses on the entire meaning of the query, not just keywords.
Pirate, announced on Aug. 10, 2012, targeted sites that had a number of valid copyright removal notices (DMCA takedowns).
Penguin, announced on April 24, 2012, targeted webspam directly. The algorithm was aimed at decreasing rankings for sites that violated Google's Webmaster Guidelines. In other words, Penguin went after keyword stuffing, unnatural link building and other black-hat SEO techniques.
Panda, announced in February 2011, is an ongoing update (that still is in use even with the new Hummingbird) that cracked down on low-quality content and content farms; it simultaneously rewards sites that contain original content and information that includes research, in-depth articles (a new Google category unto itself) and analyses with higher rankings.
Reviewing the Footage
If your website's traffic and rankings have dropped-and you have checked your Google Webmaster Tools account to rule out the possibility of a manual action penalty-it is possible that you have been penalized as a result of an algorithm change.
Most often, these algorithmic penalties are a result of Panda or Penguin. Google's Webmaster Tools provides an array of information, including analytics tools that can help break down traffic data (Tweet This!). A sudden drop off in traffic can mean a penalty; check to see if Google has announced any algorithm updates. These updates are sometimes announced (albeit occasionally a bit vaguely) on Google's own blog Inside Search. Of course, there are tools available that make this investigation a little easier, like Fruition's Google Penalty Checker. Tools such as these can help identify what it is exactly that is triggering the penalty.
Give your website an honest review. Is there an overabundance of ads? Was the copy written with the intent of filling it with as many keywords as possible? Did you purchase any links? If you answered "yes" to any of those questions, it may be a Penguin problem.
Is your content a little bit on the thin side? Does it lack any sense of usefulness or purpose? Did you purchase all of your articles from a company that may be a content farm? Well, it could be a Panda problem.
Have you received a DMCA takedown notice (or many of them)? It's probably a Pirate problem.
Getting Back in the Game
Some of these problems are simpler to solve than others. If you've been hit with a Penguin penalty, Google assumes there is some shady SEO activity going on. First things first-if you have hired an SEO company or manager to head up your efforts and you discover that they have employed black-hat techniques, let them go. Google does not tolerate these practices, and neither should any sensible company.
Removing unnatural links is a time-consuming process. But thanks again to Google Webmaster Tools, you can download a list of links to your site to find those that website violate Google's guidelines. Once found, contact the webmaster of the site in question directly and ask-politely-for them to remove the link or add "nofollow" tag. If you are unable to have the links removed, you may use the Disavow links option in Google's Webmaster Tools (an advanced option, so take care in performing this). If your site received a manual penalty - either a site-wide match or partial match - here are the steps on how to remove a manual penalty.
To reverse Panda penalties, review the content you have on the website. Each piece of content on every single page should have a purpose-if it doesn't, scrap it (Tweet This!). It is not necessary for the website to be filled with text, especially if it's littered with keywords, in order to be useful. Hire well-rounded, authoritative authors (and only a few, not an entire team) to pen your content instead of low-budget companies that only want to satisfy a word count.
Planning for the Future
After you have satisfied Google and the penalties have been removed, review your current Web strategy. With Hummingbird seeking to cherry-pick only the very best websites, your SEO strategy should focus on providing good information that users would want to find. As for staying in the Google game (and out of trouble), the best advice is still to focus on well-written, original content-where good content goes, links follow.