1. Download Android SDK: http://developer.android.com/sdk/index.html. Choose windows, Mac or Linux.
2. Unzip to where ever you like. (E.G. „c:\Program Files\android-sdk-windows\“)
3. Start „SDK Setup.exe“. Be patient, there is stuff to be loaded.
4. Chose which Android SDK Versions to install. I advise you to take all. Again: be patient.
5. In the meantime download Eclipe IDE http://www.eclipse.org/downloads/
6. Chose „Eclipse Classic 3.x.y“ or whatever most current version.
7. Unzip Eclipe, e.G. „c:\Program Files\eclipse\“
8. To install Android Development Tools (ADT) Plugin for Eclipse start Eclipse („c:\Program Files\eclipse\eclipse.exe“). Use Default value as workspace.
9. Select Help > Install New Software.
10. In the Available Software dialog, click Add….
11. In the Add Site dialog that appears, enter a name for the remote site (for example, „Android Plugin“) in the „Name“ field. In the „Location“ field, enter this URL: https://dl-ssl.google.com/android/eclipse/site.xml. Select „Developer Tools“, accept everything, press finish, mark certificate as trustworthy if necessary etc.
12. Restart Eclipse.
13. Select Window > Preferences… to open the Preferences panel
14. Select Android from the left panel. For the SDK Location in the main panel, click Browse… and locate your downloaded SDK directory. (E.g. „c:\Program Files\android-sdk-windows\“)
15. Click Apply, then OK.

Now go for your first „Hello, World!“ on Android: http://developer.android.com/guide/tutorials/hello-world.html

Reference:

• http://developer.android.com/sdk/index.html
• http://developer.android.com/sdk/eclipse-adt.html#downloading
• http://developer.android.com/sdk/eclipse-adt.html#installing
• http://developer.android.com/sdk/installing.html#components

German:

• http://www.sevo.org/2010/03/android-sdk-einrichten/
• http://www.milestone-blog.de/android-development/verteilung-der-android-versionen-juni-2010/
• http://www.milestone-blog.de/android-development/android-sdk-und-eclipse-einrichten/