The initial step you need to take is to reserve a old church or inn for the ceremony up to a year in advance. This can be crucial because many of these places can fill up in a hurry and this would drive home the fall theme. You should avoid waiting on this step because you will be found without a place to be wed.
The second step is to incorporate fall colors into the wedding ceremony. Items to avoid here are bright colors like blue and pink. You should have dark, earthy colors like brown and green to drive home the fall colors like the fallen leaves.
Your third step is to make a reception menu that includes foods usually reserved for Thanksgiving Dinner. This is important because food like turkey, dressing and mashed potatoes will make people have the warm fall feelings they love.