What's something YOU'D like to see in a game? Comedy, Action, etc.? Think about what kind of characters/personalities you'd like to meet, and what kind of sceneries/places you'd like to go (if only they existed T_T, if they do, that's good, too.) Then make that game YOU'D like to play, and watch as your imagination goes wild. (How can you get inspiration to continue if you're not into what you're making, right?)
Now go, my future flash-game maker! And good luck!