Unified Modeling Language (UML) is a great way for visualizing the design of your application or game. NClass is a free UML editor that you can download and use.
You can preplan all of your methods, attributes, properties, classes, and enums – pretty much everything related to programming – with UML. UML really helps for the next phase, which is actually to implement the prototype:
Further planning of implementations can be seen in the following screenshot:
