App and in-app pricing best practice is a moving target. Sensor Tower have a mini case study of the effect of price changes on five apps – Tiny Wings, Angry Birds, Goat Simulator, Heads Up and Sims 3. It shows the effect of price drops on the volume of downloads and in app purchases. AppDK has more guidance on how to manage your price change.
The importance of pricing is spawning services like The Loadown which can manage you app pricing based on competitors pricing, as discussed on this AppMasters podcast episode.