I ran PRs of 9:19/4:21 after coming off a cross country season with 15:47 5k XC fitness, so I can share what I did that I need helped me the most.
I went to a California HS, so my training goal was for me to peak in late May where our section/state championships happened. From Dec - Feb, I increased my mileage a little bit from XC. During XC, I was probably averaging around 40 miles per week during XC and increased to 55ish during base training for track.
I lived in a moderately hilly suburb, so most of my runs were typically 8 - 10 miles on asphalt streets. I ran a lot with teammates who were not at my fitness level, which I think helped because otherwise I would run too fast on my own. I would usually run around 7 - 7:30 pace with an occasional stop. Also, I think the hills helped a lot. I never did any formal hill workouts during this time but I do feel easy runs with lots of rolling hills (at a moderately easy pace) helped build strength during workouts later in the season.
I did a long run of around 12-13 miles maybe every two weeks. Doing weekly long runs might have burnt me out early, but who knows.
After most easy runs, I would do bare foot strides on the football field for 100m. I would start slowly and build up to full sprint. I would do about 6 of these every other day, and I think this overall was good for my mentality of knowing I still have speed in my legs (doing easy runs gets draining LOL).
I disagree with what a commenter above who said take very few days off. I took a lot of random days off. Sometimes I would run 5 days a week, sometimes I would do 6. Listen to your body and one off day or even just a shorter run never hurt me in the long run. I didn't force myself to run 55 miles per week and that number came more from an average. Sometimes I'd feel good and go 60, sometimes I went 50 or even 45.
Hope this helps!