Working on the "between books" factsheet yesterday proved to be incredibly useful. I know what the new status quo is in the city and roughly how my hero's actions have affected things.
What I also got out of it is some major inspiration for where to go with book 2. I have a tentative working title, even if it's a bit cliché, and a nice starting-off point.
Writing down what happens between two books is such a simple idea, I'm actually a bit shocked I never thought of doing it before.