Keep in mind (1) technique development (2) percentage of low vs higher lactate runs (3) running surfaces
Running faster ultimately comes down to one thing: on each and every step maintaining a footplant speed that is faster than relative ground speed.
(1) To reach each new level, you will have to develop a progressively better technique, which is likely not the technique you have now. Practice elements of an improved technique in your runs. Is it quicker tempo? Improved positive foot speed? Quicker foot plant? Relaxation of opposing muscles? Be creative. Keep it fun.
(2) Be careful not to overdo high lactate runs. Carrying an elevated blood lactate level for successive days will interfere with enzyme activity and may even damage cell walls. Easy days are important. Pool running on easy days is a great way to maintain cardio while maintaining muscle elasticity.
(3) Maintain your feel for the surface you will race on, but do the majority of your miles on grass or dirt.
Hope this helps.