Eat as soon as possible after crossing the finish line.  Research indicates that food taken in during the 15-30 minutes following hard endurance training speeds recovery, so even if you don't feel like eating, try very hard to get some food in you.  Yogurt is especially good, since it has both carbohydrates and protein, and bananas and bagels are great also.  Change into dry clothes, and DRINK, DRINK, DRINK!  Even if you've been drinking along the course, chances are that you're dehydrated.  Keep drinking more water all week long following the marathon.  Do some light stretching after the race as well, but don't push it very hard.
            The following day, you might feel a bit sore.  This is a good time to go for an easy walk, just to loosen up the leg muscles.  Do this the next few days as well.  Take it easy for the whole week, and if you feel good by the weekend, you can start up your exercise program again, but at a much lower level--nothing over an hour for the next few months.

            Congratulations!  You should be very proud; you've achieved something rare and wonderful!!!