Once you have completed the first phase you move into your Define stage.
This is where you begin collecting all your hunches and hypotheses around what needs optimising and translate this into a design experiment for your cycle.
You will collect assumptions around pain points and opportunities to delight, you will also consider the delivery model, you will collect hunches around improving feasibility, and you will think about your business model and which KPI changes will have the biggest impact on your product/optimisation.
Your outcome will be hypotheses of opportunities to optimise, prioritised hypotheses turned into design experiments to gather data and insight to test them, and a clearly defined methodology and success criteria for your optimisation cycle.
As you move through each step in this phase remember to consider our three lenses; audience, organisation and market.