A good game designer gives his players continuous challenges, where each completed level leads to another more challenging level, to keep them “hooked” on playing a game. You can keep players engaged by setting clear, short-term goals appropriate to the level of the player and to the context within the game.
A well-thought-out game design has a good structure that is often driven by a Game Design Document (GDD). GDD is to unambiguously describe the unique selling points such as the story, characters, user interface (UI), level, sound and music, and gameplay.