To begin solving the problem of how to make a good multiplayer user experience for a co-op, synchronous mobile game, I first began by sketching out thoughts, notes, and possible layouts and UI items. 

From the initial sketches, some potentially good ideas seemed to emerge. I followed up the rough first phase of sketching by refining these ideas through further sketching. Sketching allows me to explore more refined ideas cheaply.

I then played around with these ideas on my sketchbook directly by prototyping within the sketches. This allowed me to quickly and cheaply explore whether some flow ideas worked or not.

Once I'd worked out some of the basic layout and transition ideas I had on paper, I walked colleagues through my ideas to see if they made sense. Out of this, some ideas seemed worth pursuing, and others were thrown away. I began assembling a paper prototype to test these with real people.

I assembled the prototype on a large board at my desk, and then asked the multiplayer platform team at Z2 to walk through it with me to see if it made sense to them. They were able to give me feedback from a technical standpoint that helped me refine the UI flow.