Running a Marathon

Throughout the past 3/4 weeks i have been jogging with a friend around 2 to 4 times per week. This is because i hope to run a marathon or half marathon in the future for a charity that helps an illness called Lupus, a disease one of my close friend's mother suffers with. I will begin to start off with light training and become more and more intense as time progresses. I am really hoping I've got the commitment and self discipline to stick at it and hopefully finish. I was wondering is there any diet tips or exercise programmes to help me and my friend along our journeys?