Without right balance of frequency, duration and intensity plateau and or stagnation will become evident. Tips to avoid dwindling progress would include:

  1. Be consistent. Consistency with the frequency of your runs builds efficiency. At least three half hour runs will improve efficiency with out increasing risk of injury or fatigue.
  2. Be specific. Train specific to your goal. It is necessary to gradually build the duration and intensity of your run until you are simulating your race goal.
  3. Rest. Adequate rest is necessary for muscles to rebuild. The positive physiological changes you are working towards actually occur during active recovery; not actually while you are hammering it.  Overtraining can be as much of a set back in making progress as undertraining. Rest well.
  4. Pace. To reap the full benefits of the training effect, it is necessary to vary your pace i.e. interval train. When you manage your pace by applying interval training for a long enough period of time, with adequate rest in between, you build up to a stronger level: greater VO2 capacity, increased anaerobic threshold, improved economy of running, a more fit cardiovascular system and musculoskeletal system.