Consistency, not racing workouts, building miles. I will go by relative xc times rather than track because weird things always happened to me in track like the flu or something.
HS Junior 5k (40mpw): 16:29
HS Senior (60-65mpw): 15:50
Frosh 8k (75-80mpw): 26:10ish
Soph 8k (85ish): 25:20
Junior 8k (90-95): 24:57 (ran 30:20 on the track)
Senior 8k (90-100): 24:24
All this time the focus was on consistent miles, long tempos up to 10 miles, cruise intervals, long fartleks over hilly terrain, long hill reps, long runs in the 16-20 range, mileage put in between 6:30 and 7:30 pace, and doing strides every single easy day. I never left out strides, even during the summer. Summer training had a very high density of hill running. I was doing somewhere between 3-6 vo2 workouts per season, theory being that racing took care of the rest. I hardly ever went past LT pace in an LT workout, and if I ever did it was because my training pack did on accident.
Also to avoid burnout I focused on eating a lot and sleeping a lot on a regular schedule. Some ice baths, no more than 2 a week.
I still had more left in the tank, and do, but life has gotten in the way since college. Resetting and focusing to break 30 before I turn 30.