A major difference between a StoryNexus game and a novel is that the player is in charge. They make the choices. The story is about their character.
This needs to be reflected in the fiction – the player character is the most important person in the story. That’s not to say that they have an easy time, or are high status or aren’t challenged and beaten up. But the story must be primarily about the player character. Don’t fall into the trap of falling in love with another character, and having the player character around to witness someone else’s adventures.
And try not to tell the player what their character is feeling. Describe what happens to the character, sure, but stay away from telling a player that their character is surprised or elated or scared. It’s the player’s conception of their character that’s important, rather than yours.