This document provides a quick guide to designing usable mobile user interfaces. It outlines four main areas to focus on: get your basics right by staying inspired by real world examples and observing people and contexts; stick to a process like scoping your application, storyboarding, and user testing; follow design principles like keeping it clean and accentuating important information; and learn continuously about platforms, standards, and interactions. The guide gives examples for each area and emphasizes the importance of iteration and usability testing.