Sketch, establish flows, wireframe. My favorite tool for mobile app design is the index card.
Cigna’s mobile app has been a project for many years off and on. I was able to take a complex flow and sketch out each components on an index cards. As the product owner, developer and my manager came over to my desk to check out progress, we quickly moved the cards around to change the flow. We explained to each other the many options for the flow and settled on a good one. Then off to Sketch to create designs to show users and business stakeholders.
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