If you’re serious about doing SEO, you need to make sure you follow the rules to stay in the good graces of the current primary search engine. Google has several guidelines on how sites should be constructed. Follow these to keep your SEO performing well. Ignore them at your own peril.
The main reason to follow Google’s major guidelines are to avoid a penalty by Google. Google has multiple levels of penalties, but they rank into 3 major levels:
- Google #6 Penalty (also called -5)
- Google -30 Penalty
- Google -950 Penalty
They are each caused by the following.
Google -5 Penalty
This is a fairly minor penalty. This particular penalty is not fully understood, but in many cases a listing gets dropped from #1 to #6. The common explanation for this penalty is by over-optimizing for a specific keyword. So if you have anchor text from off-site links using only one particular keyword phrase (and no variations), you can encounter this penalty.
Google -30 Penalty
This is a heavier penalty, set to websites that use gray-hat to minor black-hat SEO techniques (and get caught). If Google catches you doing any of these things, you’ll get dropped 30 positions. There are mixed reasons for this penalty, but include creating “doorway” pages (where a page is optimized for just the search engines but redirects to a different page for humans), filling blog comments with spammy comments, and other only moderately evil deeds.
Google -950 Penalty
This is the big one, where Google has caught you doing something very bad, very black-hat. By being penalized 950 pages, you are sent to the last page of the listings on Google. There is no set list by Google for what will cause this particular penalty, but major reasons are having pages that are malicious (such as with phishing schemes or installation of malware), or linking to such a site. If Google feels your pages are malicious enough (and not just linking to bad sites), you can get completely black-listed and be removed from the listings entirely.
In the case that Google penalizes you, if you correct your black-hat ways you can request reconsideration. If you do this, make sure to explicitly tell Google which issues you found and corrected, and then they may remove the penalty (if the corrections you made were to the issues that caused the penalty). There is no way (currently) to ask Google what caused your penalty, and they go through reconsideration requests at their own pace. You can only check the listings after some time (usually a week or two) to see if they have removed the penalty.
To make sure your SEO stays solid and you don’t experience penalties, a recommended approach is to check that your site abides by Google’s Webmaster Guidelines.