You best bet would be to find a game, or few games, to base your game off of. Because you're starting out, it's easier to focus on how to make a game that you have a clear vision of rather than being lost in the dark trying to figure out what you're trying to make in the first place.

I would find a SNES or Genesis game that I'd like, add in some features from a more recent game and then see what happens. Figure out how to make it work, then worry about being more original for your next game.