Step one is to book a nice, historic inn or tavern to have the wedding ceremony at. You actually need to get this because it will set the mood for a winter wonderland for your wedding. You must avoid reserving a place for your ceremony that does not fit the theme of somewhere that someone would retreat to on a cold winter night.
The next step is to get flowers, like poinsettias, that drive home the special and unique feel of winter. Things to avoid here are flowers that look to much like spring or would not remind someone of winter.
Your third step will be to come up with a favor that resembles the season, such as a Christmas tree ornament. This is really important because it will give your guests something to remember your wedding by.