I have the good fortune of working with writers who come up with multiple ideas for screenplays and books and I’m often asked what’s the best approach to getting them all done.
My first advice is to date your material, don’t marry it. Before you commit to a story, spend a little time with it, get to know what’s good and bad about it. Is it the story you want to be working on right now? Is it worth your time?
Second, if you decide you just have to work on two stories simultaneously, make sure you commit to both of them equally. (Big Love not Jesse James!) Schedule time to work on both of them and commit. If you can’t then just work on one.