Really, this all depends on your current status of fitness and what level you're willing to start out at. For newer runners on our team (cross country runs 5 kilometers which is 3.1 miles), they usually start out at a fairly low mileage. After that, every week you're going to have to want to add about 5 miles to the weekly mileage. Those who are just starting usually start off at about 18-24 miles a week (2-3 a day). Eventually, you'll work your way up to the higher miles a week. It all just takes time.
Just starting out, you're going to want to run at a comfortable speed pace. Something that isn't all out but you shouldn't be able to really talk to someone else with the pace you're carrying. Later, you'll add speed runs and short distance repeats in the weeks before a race to gain more speed instead of endurance.
If you're shooting for running a 5k, this is what our coach has us doing:
Miles/Wk Mon Tue Wed Thu Fri Sat Sun
20 2 3 3 4 2 3 3
25 3 4 3 5 4 3 3
30 3 4 4 6 4 3 6
35 4 5 5 7 5 3 6
40 4 6 6 7 6 4 7
45 5 7 6 8 6 5 7
50 6 8 6 8 7 6 8
55 6 8 7 8 8 7 10
Sorry the chart came out weird. I can't format it correctly in the post.
On this, you'll want to start out at 20 and stay there for probably two weeks since you're just starting out. After that, you should move up to the next level every week.
Nutrition wise, you know what's healthy and what has alot of carbs. However, you want
complex carbohydrates after workouts. This is very important. While things like fruit snacks, candy, and other processes foods provide alot of carbs, they are simple carbs, which your body simply processes and craves more of. Complex carbs are the best you can have. Whole grain pastas, breads, and cereals; vegetables, and oats are a good source of complex carbs.
Another important nutrition thing to remember is that you want to generally try to get some carbs and protein after every workout. The carbs will restore used energy and the protein will repair muscle damage from the workout. I like to have yogurt or peanut butter and jelly sandwiches as my post run meal. Try to avoid food for the two hours before your workout though if you don't want an upset stomach. Eventually, you'll figure out your own body's needs.
This site should provide you with some good tips if you really want to run that marathon though. If you do, remember, it's more of a mental race than anything else, especially after mile 20.