When you start on the user input part, begin by writing down each thing that the user can change and what needs to happen after the change. This can help you design the user interface and specify the events required for the event structure.
It also often lets you identify things which have been overlooked or things which are never used by the user.
If you have a chance to talk to the users, ask them what is hard to do, what is confusing, what does not work, and so on, about the existing program. Oftne users have a very different perspective than the person who is writing the program.
Lynn
