I was a 30:43 10k runner in college and had big goals of running a fast marathon once I graduated. The first time out, at age 24, I trained to run 5:30 pace and ended up running 2:27:50. Over the next few years, I only got slightly faster and ran 2:24:31 (age 29).
The general themes in my marathon training were as follows;
80-90 miles/week (week after week for months). Rarely got over 100.
Most of my daily runs were in the 6:00-6:30/mile range.
Rarely ran slower than 7:00/mile
Long runs in the 18-24 mile range at 6:15-6:30 pace.
Key workouts were mile repeats (5:00), 10 mile tempo runs (5:30) and hill repeats.
I didn't over race and put my energy into training.
Preparing for a marathon meant 4-6 months of focused training with a few short races mixed in (5k - 10 miles).
Nothing fancy. Just consistent running.