Being on the first page of google is very important. Even relatively obscure keywords get a fair bit of traffic from google. On the other hand, if your site is not on the first page of google, it will not get much organic traffic. This has meant that plenty of people have tried to fool google to rank their sites high. Needless to say, google does not like to get fooled and has over time created a number of various slaps and penalties.
SEO has changed drastically since google decided to pay much more attention to backlink profiles, that is the set of links pointing to your site. Earlier, poor backlinks could not really harm your site, unless virtually all of them used the same anchor text. But nowadays, suspicious backlinks can make google penalize sites. Actually, it looks like it is the main reason that many small sites have disappeared from the first page of google.
All is not lost if your site has been slapped by google, in many cases it is possible to recover. First you need to work out why your site has been penalized. This can be far from easy, google seldom tells you why your site has been dropped. But there are generally just two reasons, either the content on your web site is very poor or your backlink profile is suspicious.
It is important to register your site in Google Webmaster Tools. Previously, it was not really worth the hassle but nowadays it is a must to have your site registered in Webmaster Tools. Under Search Traffic -> Manual Actions, you can find any manual actions taken against your site. You can also get warnings that your site may get penalized unless you take action. Nobody outside google knows what google is up to but it looks like there are two kinds of slaps or penalties, manual and algorithmic. The latter happens automatically after google has changed its algorithms. Google also have people who visits sites, looking for low quality sites such as autoblogs. Sites that are deemed to be of low quality receive a manual penalty.
Manual penalties can only be removed manually. If your site has got a manual penalty, you have to fix the problem and send a reconsidering request to google. As mentioned, in Webmaster Tools google generally tells you that your site has received a manual penalty and sort of tells you what the problem is. Unfortunately, it can take a number of reconsidering requests before google removes a manual penalty. But it is possible to get manual penalties removed.
Algorithmic penalties are in that sense easier to remove. Once you have fixed the problem, you just need to wait two weeks or so and your site should move up in the ranking. Unfortunately, it is often very difficult to work out exactly why your site has lost ranking. The two main culprits are Panda, looking at things on your site, and Penguin, looking at your backlinks. Panda penalties are relatively easy to guess, although nobody knows really what google doesn’t like. Over-optimized pages, poorly written contents, too many outgoing links and slow response times are just a few things that are supposed to trigger Panda penalties. In any case, it is always a good idea to have quality content and good response times.
Penguin penalties are generally the most difficult to get rid of. For this you really need all backlinks to your domain. Unfortunately, no tool will show all backlinks, you need to use several tools and put together your own list. Use as many tools as possible, your chances of success depends on how many of your backlinks you find. You are supposed to contact the web masters of sites from which you want links pointing to your domain removed. Obviously, it will not always be possible to get links removed so google has created a Disavow tool.
Google tells you to use the Disavow Links feature with caution, used wrongly it could harm your site. The tool itself is simple to use, you create a file with the links or domains you want to disavow, one link/domain per line, and submit it to google. Exactly how long you have to wait is not specified but it seems to take about four weeks. The difficult part is to put together the file with all the backlinks you suspect that google does not like. Obvious candidates are links from sites that have been de-indexed by google, sites in foreign languages and paid links but the gray zone is huge. You also need to make sure that you have a good variety of anchor texts. According to google, backlinks from well known spam sites are automatically ignored by google’s algorithms, so there may not be any need to panic if you find some poor quality backlinks. You may need several attempts to get rid of algorithmic penalties as well.
Sometimes, it is actually easiest to forget the old domain, buy a new domain and move the content to the new site, improving the quality if possible in the process. If you don’t care about the domain name it is certainly the quickest way. I had one site that had got manually slapped by google, after two rejected reconsideration requests I gave up and bought a new domain. I simple removed the content from the penalized site and copied it to the new domain, with a few minor modifications. It worked fine but of course I lost all backlinks, good as well as bad links.
If the domain name is important to you, it may be best to talk to people who have specialized in getting rid of google penalties. It is almost always possible to get rid of a penalty but it can take a long time, require a lot of creativity, perseverance and patience.