I heavily depends on what type of game you want to create. If you want to tell a story, you face the same problem as any story writer, and can look up advice accordingly.
Then there are stories that are only an excuse to have a game mechanic. Like the Mario games.
And on the far side are games that are only mechanic. 2048, Baba Is You and Pong come to mind.
Coming up with a new mechanic is really hard. If you have a pitch for a story, you might come up with fitting mechanics or puzzles or whatever.
But if you are bored, maybe try making a game you would like to play.