+5  A: 

Guidelines for Handheld & Mobile Device User Interface:

While there has been much successful work in developing rules to guide the design and implementation of interfaces for desktop machines and their applications, the design of mobile device interfaces is still relatively unexplored and unproven. This paper discusses the characteristics and limitations of current mobile device interfaces, especially compared to the desktop environment. Using existing interface guidelines as a starting point, a set of practical design guidelines for mobile device interface is proposed.

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+3  A: 

Microsoft has an official set of Guidelines for getting the "Designed for Windows Mobile" logo. These are a reasonable start as they not only cover one-handed (no touchscreen) operation, they also help your app to maintain familiarity for users.

Some other resources discussing the topic:

ctacke