You think a lot to graphic and sound:
In my case I need to think to data and client-server communications, then to the client interface.
Creating the GUI (and sounds) is funny!
Research for graphics and resources.
Make a concept with photoshop-Gimp
change the whole graphics because i don't like how it looks
Repeat 2 previous steps many many times
Search forums, learn how to use some tools (like texture packer, map editor, audio editor, physics engine, libraries needed...)
In my case I need to think to data and client-server communications, then to the client interface.
Creating the GUI (and sounds) is funny!