Read original post by Nick Randolph at Visual Studio Magazine
After publishing your first Windows Phone application to the Store, you'll probably wonder how that app's being used. Unfortunately, the Store itself only provides minimal information, such as the number of downloads. It's important to add telemetry code during an application's development, rather than trying to retrofit it later. Exactly what events you'll want to track will vary depending on your application, but you may want to start by recording when an application launches and terminates, when it's suspended and resumed, and perhaps recording which pages are viewed and for how long.