If you're not already strength training, do so. A strong core is more important than you think to get you through your training and the race. Also, read up on nutrition for marathoners so you can start thinking about your meals and menus now. I was surprised that most nights when I would go to bed I would suddenly get hungry and get up for a bowl of cereal. I realized I wasn't eating enough during the day. Allow yourself a week or two wiggle room in your schedule case you get sick, injured, can't run because of holidays, or life in general. A lot can happen in 16 weeks!
Enjoy your training.
"God gave you your body as a gift, so you should take care of it." - My Mom