The HOWTO at Android site describes a number of have-to-be-easy steps to install the ADT.
In real life however many people including me end up with an error message like this:

Missing requirement: Android Development Tools 12.0.0.v201106281929-138431
(com.android.ide.eclipse.adt.feature.group 12.0.0.v201106281929-138431)
requires 'org. ( Read more... )