There is probably not a single person involved in running who would not like to improve their results – including endurance.
This can be done using the method described in this article.
Runner's World Race manager, whose name is, as you might have guessed, Bart Yasso, suggests the following training option.
He advises running 800 meters at the pace you plan to run your first marathon.
Let's give an example: if you plan to spend 4 and a half hours to complete your first marathon, then you should spend the same 4 and a half hours to complete 800 meters.
Try following Yasso's plan by running once a week.
Start with four to five 800-meter intervals at your goal pace, and gradually increase the number of intervals, one each week, until you're doing ten.