Help with beginnings

I have a story all worked out so far: I know the gist of how my plot will go, and my main characters are mostly fleshed out at this point.

However, I am COMPLETELY stuck on how start it. Any help?

Story: Crazy Jane
Main Character 1: Heather Lewis
Main Character 2: "Crazy" Jane Murphy

I might start it with Heather arriving (or driving to?) the reformatory and thinking about how she got there. Then you can dive into a bit of the backstory without overloading it and still have the action start pretty early on.