After plotting my user flows, I started by sketching they key screens from them. Initially, I just went through the flows and quickly sketched each screen until I was happy with each. It’s a similar approach to the crazy 8 technique which I find works better for me. There’s a lot of screens, like Question/Answer screens, that have established best practice patterns, and sketching 8 would be a waste of time. Equally, I find it useful to sketch them once or twice to start thinking of any unique parts I’ll need for the project.
After the initial round of sketching, I identified some of the key screens that would be important to get right, and went back to do more detailed versions of each. For some screens, I focussed on proportion, but some were more feature and function based. Overall this gave me a good basis to work from for my wireframes.