I have been making games for about 7 years now, the last 4 which I have spent as a game designer. I have learned a good deal about being a game designer in that time, and I thought I'd share a few lessons that I think have made me a better designer.
Always Champion the Best Idea
One of the big differences between a junior designer and a senior designer, is the senior designer will try to champion what they think is the best idea for the game, not just their own ideas. A seasoned designer is able to spot and recognize good idea for a solution to a design problem, and they are comfortable with the fact that that solution does not have to be their original idea. Game development is collaborative effort, and everyone on the project has ideas on what direction the game should take and what makes the game fun. A designer listens to their team, gets their team's thoughts and feedback, and critically examines it. The job of a designer is to take the seed of an idea from where ever they get the inspiration for it, and make it grow into fun and polished part of the game. Sometimes that idea comes for the designer's own mind, but more often than not it comes from somewhere else.
Appreciate All Disciplines of Game Development
Game development can be seen as six general disciplines: Art, Audio, Design, Engineering, Production, and Quality Assurance. Learning to appreciate all disciplines a designer is critical. A designer works with some one from every discipline at some point throughout development. Having a fundamental understanding of each discipline helps foster good communication, which in turn will create a better end product. For example, if a designer has a better understanding of color and contrast, they can better understand where an artist is coming from when explaining their vision for lighting in a particular scene. The designer can give intelligent feedback to the artist about the lighting, explaining how they see the lighting working with the desired design for the game, and foster a constructive discussion where both art and design work towards delivering a strong presentation for the scene. As a designer, have a hungry mind and be eager to learn about the five other disciplines of the game development. The better a designer can communicate with their team members, the better chance the team has of seeing their vision for the game become a reality.
Live a Full Life
Get out there an live. Experience new things and have interesting stories to tell. A big part of game design is about delivering an awesome and captivating experience to the player. The more life experience a designer has, the more experiences they have to draw on for their designs. A designer could be sitting down to map out a level for a multiplayer shooter, and the idea for the level starts with inspiration from some city streets the designer was wandering through last weekend. The level may end up looking nothing like the city streets the designer walked through, but the inspiration for the idea came from real life experience. So as a designer, as human being, take breaks from playing and researching games and go experience some real adventures. It will help refresh the mind and inspire new ideas.