Try using the ‘seven basic plots’ as a handy jumping off point for RPG stories. Obviously you’d need to take into account the tone of the game your playing.
Overcoming the monster: The protagonist sets out to defeat an antagonistic force (often evil) that threatens the protagonist and/or protagonist’s homeland.
Rags to riches: The poor protagonist acquires power, wealth, and/or a mate, loses it all and gains it back, growing as a person as a result.
The quest: The protagonist and companions set out to acquire an important object or to get to a location. They face temptations and other obstacles along the way.
Voyage and return: The protagonist goes to a strange land and, after overcoming the threats it poses or learning important lessons unique to that location, returns with experience.
Comedy: Light and humorous character with a happy or cheerful ending; a dramatic work in which the central motif is the triumph over adverse circumstance, resulting in a successful or happy conclusion.
Tragedy: The protagonist is a hero with a major character flaw or great mistake which is ultimately their undoing. Their unfortunate end evokes pity at their folly and the fall of a fundamentally good character.
Rebirth: An event forces the main character to change their ways and often become a better individual.