Prerequisites

• Your ROM needs to support signature spoofing, see Signature Spoofing
• In case you had the Google Play Services previously installed, remove all updates and the packages in /system/priv-app of the Google Services: GmsCore (PrebuiltGmsCore, PrebuiltGmsCorePi, PrebuiltGmsCorePix), GoogleBackupTransport, GoogleFeedback, GoogleLoginService, GoogleOneTimeInitializer, GooglePartnerSetup, GoogleServicesFramework, Phonesky and Velvet. In case you forgot to remove the GmsCore updates, you can manually remove these using adb uninstall com.google.android.gms. After that, reboot your android device - all privileged GAPPS should be removed.