ADT setup on Eclipse IDE on Ubuntu

Custom plugin for the Eclipse IDE, called Android Development Tools (ADT). 

If you need to install Eclipse, you can download it from http://www.eclipse.org/downloads/. 
Android recommend the "Eclipse Classic" version. 

Download the ADT Plugin
Start Eclipse, then select Help > Install New Software....Click Add, in the top-right corner.
In the Add Repository dialog that appears, enter "ADT Plugin" for the Name and the following URL for the 

Location: https://dl-ssl.google.com/android/eclipse/    >>  (Click OK)

Note: If you have trouble acquiring the plugin, try using "http" in the Location URL, instead of "https" (https is preferred for security reasons).In the Available Software dialog, select the checkbox next to Developer Tools and click Next. In the next window, you'll see a list of the tools to be downloaded. Click Next.
Read and accept the license agreements, then click Finish.

Note: If you get a security warning saying that the authenticity or validity of the software can't be established, click OK.When the installation completes, restart Eclipse.

Configure the ADT Plugin
After you've installed ADT and restarted Eclipse, you must specify the location of your Android SDK directory:

Select Window > Preferences... to open the Preferences panel (on Mac OS X, select Eclipse > Preferences). Select Android from the left panel.

You may see a dialog asking whether you want to send usage statistics to Google. If so, make your choice and click Proceed. For the SDK Location in the main panel, click Browse... and locate your downloaded Android SDK directory (such as android-sdk-windows). Click Apply, then OK.

If you haven't encountered any errors, you're done setting up ADT and can continue to the next step of the SDK installation.

Source: http://developer.android.com/guide/faq/troubleshooting.html#installeclipsecomponents