This hack is great to increase your downloads. For Android use AdModb which cross-promotes your app for free, this is the guide on how to do it. For iOS Apple works with Search Ads, this system helps your App rank higher, it is a pricier option, but you can get free credit to kick it off. For Android and iOS, you can use AdMob Mediation is the solution for Google and AdSense for mobile, this lets you have ads on your App, this is how.