Long distance runners, at least all of the ones I know, eventually become obsessed with time. In fact, they seemingly define themselves with a number, split, or personal best. Whenever they hit the road, the primary goal in the end is always "the clock." They train hard to improve the time it takes to cover the next distance, and they set goals based on how long it will take. In the end, everything revolves around the mighty clock.
Therefore, when figuring out a way to workout effectively, in a way that not only has some mental stimulation but also a strict attention to the pursuit of your goal, you have to devise plans that blend the idea of time and challenge. Simply setting up and running the distance you want, timing it, and then trying to beat it the next day never really amounts to much, especially when it comes down to staying fresh. So, rather than doing the same old thing people have done for ages, try this small variation. Not only will its small increments keep refocusing you, but the end result will give you a realistic perspective on what you can expect come race day.
Start by breaking down your distance into quarters. Grab a stopwatch and head to the track. For example, let's use a mile. Do a quarter mile as fast as possible. Record the time while resting for 90 seconds. Repeat this pattern for the other three quarters, each time noting the time. In the end, add up all four times and divide by four to learn what you can expect to be your race time. This style will not only provide you with good timing feedback, but its broken down manner will let you repeatedly regain focus and mental energy. It may seem so simple, but remember that most training, at its core, is best when it is basic and clean. Best of luck.