Adsense Knowledge Base

By banning, I mean Google excludes your site from indexing and kicks it out of the databases from showing any results. This is primarily because of:

• Hidden text - text rendered the same color as the background so that what search engines see on the page is not quite what visitors see, giving webmaster the chance to cheat a little bit on content, usually stuffing the page with keywords that provide no value at all.
• Markup spamming - another way of craming keywords on page, including page title spamming, image alt spamming, meta infomation spamming and so forth.
• Excessive linking to already banned sites - while one or two links to banned sites will affect your page ranking in Google (this is also one of the reasons of sudden SERP drop), too much linking to these sites could also get you banned. This is usually referred to as 'Bad Neighborhood' which you should avoid by checking your outbound links regularly to see if any of the linked sites fall banned by Google.

Never ever go with these ranking methods or fall in Bad Neighborhood, as veteran SEO experts say to newbies.

Note this is not a full list, anything that infringes law may well lead to banning.