How to install the Android SDK and Eclipse on Windows and Ubuntu, Step-by-Step has a basic tutorial on how to install the android SDK and the requirements for the project. However, people like me (who don’t want to use too much brain power after coming back from work tired) need pictures and a detailed step by step guide. I found two great tutorials searching the internet.

One for Windows users-
And this one for Ubuntu Linux users-

Note: while installing the ADT, if you get an error saying : “No repository found at” try changing the https to http. If for some reason it still doesn’t work, you can download the ADT here:

In Eclipse 3.3, click New Archive Site….
In Eclipse 3.4, click Add Site…, then Archive…
Browse and select the downloaded the zip file.

or check here