A clear plan is the beginning of a great design. Step through the experience from the users point of view. What are they doing? What can they also do? How do they change something? What is not needed? What changes are required for different display sizes? We have guides and tools for this.
It’s the little things that can make all the difference. Too small and too big can make or break a games success. But, if you plan for that and check the design, display sizes and formats, you’ll see it quickly. With simulation and testing, this is avoided.