When your website has been penalized by Google, it means that it will no longer show up in search results on Google or Google's partner websites. If your website is your livelihood or some part of it, it is important to get your website back into the search engine's site indexing as soon as possible.
Determine the Cause for Penalization
The first step is to determine why your website has been penalized by Google. Go to Google Webmaster Tools and register your website if you haven't already. You will be asked to verify your website by uploading a provided meta tag or HTML file to your website. Once your website is verified, you can use Google Webmaster Tools to check for messages that may point to a quality issue with your website that is causing it to be penalized by Google.
A short list of items that can cause your website to be penalized by Google are using hidden text, duplicate content, keyword stuffing, bad links, and participating in link farms that link your website with poorly ranked or otherwise irrelevant websites. If you are working with an SEO company and your website is penalized by Google, check that they aren't using unfair practices to falsely manipulate your Google PageRank.
Lifting the Penalty
Once you determine why your website has been penalized by Google, you need to find out how to fix the quality issues and get your website back into Google search engines. First, read over the latest version of Google's Webmaster Guidelines. The Quality Guidelines are the most important topic to find out about any illicit website practices that may lead to your website being banned.
Once you are positive that any quality issues with your website have been resolved or removed, then you can file a reinclusion request via Google Webmaster Tools. Unfortunately, there is no set date for Google to review and reinstate your website in its search engine results. But, if you wait for the penalties to be lifted on their own, it could take up to a year to be back in the search results!
Keeping Your Website in Good Standing with Google
To be certain that your website is not penalized by Google in the future, you should familiarize yourself with Google's Webmaster Guidelines, and make certain that your website complies with these guidelines. Aside from not violating Google's quality guidelines, the best way to insure that your website will show up in relevant Google search results is to provide unique, useful, quality content on your website.
If you discover that your website has been penalized by Google, you want to resolve the issue as quickly as possible. By using webmaster guidelines and tools provided by Google, you can determine the issue, fix it and request that your website be reinstated.