You will need to look pretty much exactly one year in advance. There are enough flights available to find something that will work, but you must check a year in advance. Good flights, especially nonstop flights go fast.
I booked our summer 2015 flight in the summer of 2014. Flying nonstop on delta from Seattle to Paris, return from Munich with a stopover in Atlanta.
One thing I wish I had known is that you don't have to book the return flight at the time you book your outbound flight, which allows you to book your outbound exactly one year in advance.