Thank you for your commitment to service.
Stay in shape.
Exercise.
Those two are extremely important. Getting into a habbit now will save you a LOT of grief. Also - practice ironing and shining shoes!

Don't worry about your schooling, or your past abilities. You are chosen to be a nuke for a reason!

Good luck, and if you have any questions this board is pretty good to learn from. Most of your questions should be answered really.