How can I sign an application for Android?
If you already have your.apk ready and need to sign it to publish it on Google Play, these are the instructions to follow:
http://developer.android.com/guide/publishing/app-signing.html
After signing the application, you must align it with zipalign:
http://developer.android.com/guide/developing/tools/zipalign.html
Aligning the application will optimize the use of the app’s resources and allow it to function with more speed.