Before you start your A/B testing, you need to identify the behavioral insights that are relevant for your product and your users. You can use various sources of data and research, such as user feedback, surveys, interviews, analytics, competitors, best practices, and academic literature. You can also use frameworks and tools, such as the Fogg Behavior Model, the Hook Model, or the BJ Fogg Tiny Habits Method, to map out the factors that influence user behavior. The goal is to find the key pain points, goals, motivations, and triggers that you can address with your A/B testing.