In Career OnDemand, we designed every use case Mobile First. We painstakingly created prototypes for every sea level use case for the employee view and manager view. It helped us focus on the most important things, clarified the purpose of a use case and made the use experience significantly better.
When we transferred the mobile first design to the web, the main button that showed up on the mobile screen was displayed in bright orange color in the web page to indicate the most probable action to the user. It was received very well by users. I'll keep you posted.