The obvious question are:
1: What do you hope to accomplish with your game?
2: Has what you want to do been done before? (Likely)
3: Can you improve that? (Always room.)
Research. I would call this the ultimate necessity. The game market is full of games. Some very similar, some very different. The last thing you want to do is reinvent the wheel. Not only are not doing anything new in that case, you are stepping on someone else's toes. Not only is plagiarism karmicly bad, it is legally bad. You don't want to go there, not even by accident.
First research the market and see that your idea isn't already out there. If not, wallow it it.