Using the Eclipse IDE, you can generate the hash the moment you export your project to an APK by accessing File > Export, selecting Export Android Application and on the screen following your project, you will have something like this:
After generated, on the last screen you will see a "Certificate fingerprints", which are in MD5 and SHA1.
With this SHA1, just you access your Google Developers Console, in your project and add this fingerprint on credential "Key for Android Applications" existing, which you use for debug mode. Remembering that you do not need to create another credential, just add a new line with this SHA1 generated for production.
For you to test this APK, just install in your device he already owns the new Keystore production, the same that you will use in Play.
Which IDE you use?
– Paulo Rodrigues
@Paulorodrigues Eclipse
– Marckaraujo