Becoming a good Designer takes years of work and practice. However, anyone can quickly become a good-enough designer by following some basic rules and carefully observing what they build. The video above covers some of the most important design principles that you should observe when doing your design.
Another way to get good-enough designs quickly is by copying how the good apps do it. If there are already popular apps that do something similar to what you want to do then you should study them carefully.