That's a great question, Ying! If you already have a product, it's time to ask: do we have a clear and agreed upon conceptual model? Does everyone on the team know exactly what the objects are in this system and how they all connect? If not (you wouldnt be alone) it's time to reverse-engineer and do that work. Identify those valuable things, their connections, the CTAs, and the attributes of each object (that's the ORCA process that I teach!). Once you have that, you can start identifying places that your current product does not reflect and reinforce your conceptual model. Do you have 4 different for that all represent a PERSON object? When you could have just 1? Do you have a generic card that you shove various kinds of objects in, making those objects hard to identify? Once you have the conceptual model, you can basically audit your current product for misalignments, then update your product to align, then update the design system to reflect that alignment as you move forward!