From my personal experience, I have been submitting applications built with Xamarin to the iOS App Store and Google Play for quite some time. After delivering nearly 50 mobile applications totaling millions of downloads, a lot of lessons are learned about what makes a mobile application successful or a failure. Xamarin apps are indistinguishable from Java or Objective-C apps to the end user, so you can make your app successful by following the same patterns as standard iOS or Android applications.
There is quite a bit you can do to make your app more successful. Here are some tips to follow: