Best advice I can give.....
NOTHING NEW ON RACE DAY!!!
Wear the socks, shoes, shorts, shirt and hat you wear for training.....Trust me, if you want to cross the finish line don't buy anything new after about a month beofre the race.
Don't go crazy warming up at the startline. Those people are wasting their energy. Just jog around for about 35 seconds and stretch out a little right before they fire the start pistol.
During your training, go the distance. If you say you are going 10 miles today, go 10 miles...If you have to walk after every mile, so be it. Just go the distance and forget about how long it takes.
In the race, I run until I get to a water station, and take a leasurely stroll and sip my water slowly and rest. Many marathoners take a walk after every mile. walk when you WANT to not when you HAVE to.