This tutorial shows that how to fix and get re-indexed by google if your website has been removed from Google index.
This problem is called " penalized from Google". And the penalization depends on some factors:
The main factor is cloaking/redirection.
So, if you believe your website penalized by domain redirection or cloaking you must look at these things:
Remove any Ads Which Redirects Your Website to External Sites
This is a must-do thing that your website may be applied to advertising system which redirects your homepage completely to a different page.
Google Machine Automatically blocks these kind of websites...!
This is mostly happened to adult websites if they are added some kind of mobile/desktop redirection codes by Plugrush, Juicyads, Ero-Advertising ads etc. So simply remove this codes from your website. After that, send an e-mail to firstname.lastname@example.org by mentioning you are now google-friendly.
Remove/Solve Any Hacking Attempts and Ads Viruses on your Website
This is also caused cloaking/redirection from your site to other spammy sites. So if you remove any hacked template from spammer codes and made your site clean then simply re-apply by sending mail to email@example.com and also by "Request a Review" on Manual Actions section in Google Webmaster Tools.
There are also some other spam actions may be applied by Google i. e. spam external links, automated pages, unnatural behaviors, lots of link soups on one page, duplicate contents etc.
You must read Google's TOS in order to avoid these kind of things.