Advances in mobile technology and mobile applications (apps) have opened up an exciting new frontier for behavioral health researchers, with a "second generation" of apps allowing for the simultaneous collection of multiple streams of data in real time. With this comes a host of technical decisions and ethical considerations unique to this evolving approach to research. Drawing on our experience developing a second-generation app for the simultaneous collection of text message, voice, and self-report data, we provide a framework for researchers interested in developing and using second-generation mobile apps to study health behaviors. Our Simplified Novel Application (SNApp) framework breaks the app development process into four phases: (1) information and resource gathering, (2) software and hardware decisions, (3) software development and testing, and (4) study start-up and implementation. At each phase, we address common challenges and ethical issues and make suggestions for effective and efficient app development. Our goal is to help researchers effectively balance priorities related to the function of the app with the realities of app development, human subjects issues, and project resource constraints.