I'd recommend consuming a variety of different genres of video games. Getting as much creative input as possible gives you a solid basis for developing your own ideas. Nowadays, people are able to build awesome Jump'n Runs only because the game mechanics have already been established by Super Mario Bros.
Another great habit is writing down all of your weird ideas, even the weirdest ones, and just let those ideas rest for a while. After having gathered many of them, you might see connections between them that allow for unique gameplay.