Many popular games are developed based on some famous movie shows, historical events or sports. This may serve give you some idea to start of the storyline for your mobile game. However, the most essentials elements to observe are that games are meant to be challenging, fun, and entertaining for games players.
Another factor to take note is that mobile games are different from normal PC games as they are often played at odd moments, e.g., when waiting for a bus, traveling on a train, or even during boring parts of a meeting. Therefore, mobile games should be quick and easy to start and navigate. They should be easy to understand, not just in terms of letting players quickly grasp the procedures and processes used in playing, but also with regard to the concepts surrounding the games – the aims, risks, challenges, and rewards.
Games should be challenging — but not impossible to win. Players are bored with easy games but quickly abandon those where they see no hope of winning, reacting quickly enough, improving their score, or getting to the next level. Challenges will vary according to context: some are immediate and visceral; others involve developing a complex strategy over time. If these challenges can develop and grow as the player develops skill and plays again and again or moves to new levels, then the game will remain compelling.
A good storyline should based on the above factors and as well as helping you to establish the landscape and game characters to your the game world. Storyline is visually illustrated through a storyboard with scenes of rough sketches and visual layout of the entire game. This serves as a reference or "blueprint" for your game's story when you get into heavy development.