A very interesting article about game design and how to become a game design it will explain some of the pitfalls that people usually do when trying to become a game designer.
one of the first things that you actually need is to read as many books as possible reading will open New Perspectives on what you can do with game on what you can do with game design.
The second thing that you have to do is to practice as much as you can, the more practice with prototypes, the more , you will be able to build correctly mechanics and how to link them with other to build interesting and fun new systems.
Second,Search play as many possible games as possible, the more you play, the more you are able to get references about mechanics, about how other designers implemented their own.
Third, creativity requires culture. Without culture you will not be able to create anything. With an empty you will have empty ideas. Read, watch moves, visit museums, travel… the more you will get into your head, the more you will get from it.