Here is a great article from Yahoo User Interface blog: Challenges of Interface Design for Mobile Devices. Many good points mentioned and applies to most UI design cases.
The single most important concept to master when designing mobile device interfaces is “context”. The context in which an application is used and the context of how information is input are both key issues; each must be understood before a well crafted design may be implemented. When these two notions of context are explored, it becomes clear that designing for a mobile device can lead to a solution that is worlds different than its desktop equivalent.