You probably already know what kind of program you are going to write. If not, put this book away and do some thinking first. Without a clear idea of what you want, it's hard to do something about it. Once you know what general kind of program you would like to create, you also need to figure out who the program is meant for. This can be something as general as 'desktop users' to something as specific as 'Haiku Web Developers'. When you know who the main users of your program will be, you can make certain assumptions about what your users know. You can't necessarily expect a musician to understand how to effectively use a 3D modelling program as advanced as, say, 3D Studio Max, but you can expect them to have skills which lend themselves to using a program for writing music.

Depending on how concerned you are about details, you may even want to create a user profile -- a fictional idea of an example user. This can consist of just one or two sentences or can be several paragraphs. A short user profile contains the person's first name, occupation, level of expertise, and what kinds of things they want to be able to do with their computer. One thing to be sure of is to make the user profile believable -- like a person you might know. In fact, when you design your app, it may be helpful if you know someone who fits into the target audience. You don't want to design your app for that person specifically, but, rather, someone just like them.