1. First, in the Play Store, you have to make sure you have the newest version of the “Google Play Services”, since this is new functionality.
2. Now, go into the settings and tap “Google” and then “Ads”. Tap “Delete advertising ID” and finally confirm with “DELETE ADVERTISING ID”.

That's it. While many apps will still continue to try and track you against your will, you have at least made it a little bit harder for them.