The best way to learn game design is to play games and to keep making games. You can also watch YouTube videos and you can read books about game design, but in the end you only become a better game designer by making games. When you are a new game developer remember to make small simple games. It is also important to remember that it is okay to make mistakes and it is better to make bad games then it is not to make any games. 

I wish you good luck with your game development.