Review the list of competencies (here) and make a mental note of which ones you have already mastered.
Be prepared to discuss examples of controllers around you. For each system that you can identify, make a mental note of the following characteristics of that system:
CV - Controlled variable: what is it trying to maintain, optimize, or control?
MV - Manipulated variable: what is it changing to achieve the control objective?
Disturbances: what may cause the controlled variable to deviate from the desired target?