I have designed about 30 applications from Commodore 64, Amiga, BBC Arhcimedes, Windows 3.1, n64 through to Vista and Embedded deivces
1. Do you have a vision or not? And who is going to use it.
If you don't then use a committee method to design your UI. Say bye-bye to what you want.
1. If you do have a vision then get your needs/features down on paper
2. Define the platform/platforms you are planning your application to run on. (things like screen aspect, minimum/maximum resolution and input device are very important considerations.
3. Start to mock up designs and position the features you are planning
4. Start to create working mock-ups of key interface elements
5. Start to get feedback on the two or three ideas you have (try getting people to see the idea you like the best - explain why)
6. Do a prototype (even if it ends up as a commercial prototype)
7. Evaluate the issues people have and the way people use it. Create a new version if your prototype is unusable - otherwise let it grow as much as it can.
"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts." -- Bertrand Russell