Genuinely new (game) ideas are rare, most good ideas are born from a fusion. That's why "scenes" succeed, that's why non-homogenous teams are more creative.
Break down your favorite games into components and build your mechanics library.
Most game mechanics can be simplified down to a model, a card game (i.e. slide about Gone Home).
If pulled out of traditional context, a deck of cards can be used to build a house, as a throwing weapon, for fortune telling etc.
Adding a simple statistic can create a new game mode or genre, i.e. adding a timer gives you a time attack mode.
Players added a "fast" mode (speedruns) to games where the game designers failed to notice this opportunity.