Get yourself a good pair of wool socks, and a running shirt, both of which will serve to get the sweat away from you rather than stuck to your body. Also a good pair of running shoes. Don’t skimp out here – if the shoes aren’t designed for running, the blisters your feet will develop will sideline you very quickly.
This may be obvious, but… “train”. Get out there and start running, at least every other day. Get yourself to the point where you can do maybe 23 miles in a single session, in whatever the pacing requirements are. You don’t need to run the full 26.2 before the “real” race, but this isn’t the kind of thing you can just do without any preparation
Be sure to think about your fluid intake—find out what they’ll be serving at the water stations (probably lemon-lime gatorade, but find out for sure) and then make sure to train at least a few of your last long runs using that, so you’ll be used to it.
Don’t wear or do anything brand-new on race day, your clothes, your shoes, socks, your drink, your pace, you food, your general routine should be as close to normal as possible to avoid anything catastrophic.
Set goals for yourself, as well as time spent running and mile commitments. Convince yourself that you actually need to train, stretch, eat right, and get out there and run, in order to be sucessful. Set your mind to completing the marathon, and no matter what, don’t quit.
Don’t forget to taper! A lot of people think that slowing your training and shortening your mileage right before your marathon is a bad idea, but it’s important to be “fresh” on race day.
I’m not sure what your training regimen is right now, or if you are just starting… nonetheless, it’s important not to give yourself an over-use injury early on in your training with too much enthusiasm. Build up your mileage slowly during the initial training session.
I always thought it was helpful to have two pairs of running shoes. You can alternate which ones you run in- this will greatly reduce the wear on your feet and help prevent blisters and other nasties on your feet.
You can also use foot powder to help keep your feet dry when you run if you are “foot sweater”.
Make yourself a training schedule with target mileage throughout the cycle so that you increase your distances at appropriate intervals.
If it’s your first marathon- try a “run/walk” Get a watch that does intervals- I do 8:00 minutes of running and 1:00 minute of walking, this allows my body to store up energy early in the race so that I can finish strong. Also gives the 1:00 minute of slowdown for supplements and hydration.
Also- I swig pickle juice pre and post run, great for replenishing electrolytes!