There are also two fantastic tutorials available in the mobile dev center.  The first provides a walkthrough of the basics of configuring your iOS app for push and sending push notifications.  The second details how to use a table to store APNS tokens that can then be used to send push notifications to an app’s users.

Just as important as understanding how to use these push notifications, is understanding when to use a push notification versus an SMS versus an email.  The easy answer is that it depends on the app.

See this informative blog post in it’s entirety at http://blogs.msdn.com/b/windowsazure/archive/2012/12/10/best-practices-for-using-push-notifications-sms-and-email-in-your-mobile-app.aspx.