First you need to have an .apk online. Doesn't have to be live but you need your signature/footprint to link you rgame service to the app. If you have an apk uploaded you can go to google game service and link it to an existing app. It will show you all your possible apps.
The you should integrate cranberry's game plugin. That gives you simple events like "submit score" and "open leaderboard". If you set this up you need to give it the "highscore id" shown in your google games setup. When you export it to intel xdk you need to add your google app id to that.
It works very well.
Is this still the preferred way of loading the google games leaderboard? It seems easy enough to follow, just wanted to make sure there wasn't a built-in way of doing this now like there is with AdMob?