Part of race preparation is running. Well those are wise words that definitely need some elucidation.
In a macro sense, everyone should understand that if they want to run a road race they need to prepare by running. If the race is more than a 5k they will have to run a lot. If the race is a marathon, they will have to run 40-60 miles per week for many many weeks. That's a LOT of running.
The accepted method for accomplishing a major portion of these miles is to run one very long run each week. For a race that is 26.2 miles, the longest training run should be a least 20 miles. A good training plan will include about three of these 20 mile runs. This milestone is only reached by steadily adding distance to your weekly long runs, (never more than about %10 more than the previous long run).
Today I ran 18.21 mile in 2 hours and 39 minutes. It was a challenge, as all long runs are for me, but I was well prepared and did not suffer. I feel great and with my scheduled rest day tomorrow, my body will be ready for my next training run on Thursday.