Support user data input
You should support data input for your users as much as possible. This could be as easy as opening the numeric keyboard for a user to type a phone number in a field or capturing data using other means, such as GPS, a Bluetooth enabled sensor, a camera, or an accelerometer. Limiting the data that users need to input can reduce the burden on users and greatly improve the usability of your application.
Another way to support user data input is to make sure that you combine similar input operations together in the flow of your application, so that users don't need to change input modes or navigate to another screen. For example, a mapping application might allow users to place landmarks on a map. You could allow users to access a menu, choose a landmark tool, reactivate the map content area, and then place the landmark. But a better solution might be to allow users to simply touch and hold the desired map location and have your application place a landmark pin at that location after a few seconds.