The designers of the videogame Civilization at Firaxis said they had a 3-thirds design budget for each sequel:
* 1/3 you keep the same, keep it familiar for those who know previous games
* 1/3 you improve on iteratively, gotta make things better someplace
* 1/3 is completely new, like the borders in Civ4, or the Hex grid in Civ5. This is the risky stuff
I think it's a nice and easy heuristic, ensuring you have a stable foundation while offering opportunities for creativity, and it can apply to many other fields than game design.
* 1/3 you keep the same, keep it familiar for those who know previous games
* 1/3 you improve on iteratively, gotta make things better someplace
* 1/3 is completely new, like the borders in Civ4, or the Hex grid in Civ5. This is the risky stuff
I think it's a nice and easy heuristic, ensuring you have a stable foundation while offering opportunities for creativity, and it can apply to many other fields than game design.