Only general advice I'm afraid. Before all else, check what the competition is capable of and try to find out which part of the functionality is the most important for the user. Having a lot of very snazzy functions, but missing out on some basic important ones will not be good. For example a word processor that allows you to use lots of fonts, but does not have "find and replace" function.

Try to think like your end user and not like a programmer. How will your end user be using the program and how can you make the work for the end user as simple as possible? Are there things you could automate for the user that save (typing) work?