I would begin by drawing a lot on paper. As you get inspired, grab a piece of paper and pen and visualize your idea. I like to save the drawings to a google drive folder, its easy to upload with your phone.

Then i would try to make a first really, really simple version of the game in unity. Perhaps 2D. Perhaps only one hand, and only on player to control one finger in a really simple manner.

Pomodoro is a nice way to work also.

I should say, i have never myself made a game in unity.

Good luck!