Instalando Plugin ADT no Eclipse

Eclipse usado: Eclipse IDE for Java EE Developers.
No menu do Eclipse clique em: Help >> Install new software...
Clique em add e informe os campos:

Name: Android Plugin
Location: https://dl-ssl.google.com/android/eclipse/

clique no botão "OK".

(help>>install new software >> add)

Reinicie o Eclipse e pronto.