Do you have a common element to all your games?
I find this question pretty easy. My colour scheme is near constant. It’s approximately… a black background with purple, red and blue on top. So they’re all banned*.
Designwise I plan to shove the theme into boxes it might not fit – board games, non-violence, whatever I walk past in the street (mailboxes?), movement systems … see what interesting things come out.
Toolbox: Unity3d SublimeText Blender GIMP Piano NoisyThings FreshAir SufficientSleep CoffeeForWhenThoseToolsBreak
*Mostly banned. Sort of.