When you design a Qt application for Symbian devices you must make various design decisions such as what technology to use for the user interface and what kind of services your application will make available to other applications.
The cross-platform application development framework of Qt offers a wide variety of techniques for designing and implementing the UI for your mobile application. They cater for various kinds of applications and use cases. You can also mix the techniques to create the UI required.
For more details on UI design guidelines, refer Selecting the Optimal UI for your Qt application on the Nokia Developer portal.
Before starting application development, analyze and define the requirements, scope, and functionality of the application to ensure efficient functionality and a smooth user experience. Design the application for a single purpose and analyze how it can best serve its users. Mobile devices have been designed for use on the go. Keep the characteristics of mobile devices in mind when you design applications for them.
For more in-depth guidelines on design and usability, refer Design and User Experience Library on Nokia Developer .