I'll start with the universe;
-Try to organize it chronologically(Creation > process > present) while mentioning the creatures on it as needed
-Since its a game, figure out the player perspective, and how it makes your universe better.(First/third person or top down depending on your game mode)
-Have an idea of what the gameplay is like; for example you mention how the player can travel between islands, but how is he actually playing the game?
-What is it about your universe that makes it different?(USP)
Story:
-What is it about the story that makes it fit with this universe?(Focus on USP's)
-Try to follow the heroes journey when you write such a story to make it more interesting. And you get plus points from the trainers for saying you followed it.
-Make it more dramatic. The summary is supposed to be short, but it has to show it is perfect for the universe

Universe is more important than the story because you can change the story at any time, however the universe is difficult to change.