Obviously this won't really apply to you since you're only going into 9th grade, but I didn't break 5 in the mile until my 9th year of running. I set a 5:15 1600m PR in my first year, and finally, a couple years ago, I figured I needed to break that, with the goal of breaking 5. So I set aside a couple months to focus on speed training. However, I don't think I was able to work on the speed as much until I built up my strength, and I had done that with a high-mileage marathon training cycle. Anyway, I did a bunch of 200m repeats and 400m repeats, treating the 200s as almost-sprints, the 400s at either goal mile race pace or slightly under. Tempos are good too, they can help build strength. Anyway, two years ago, I PR'd twice at 1600 from these workouts, going 5:12 and then 5:06 two weeks later. Not quite sub-5:00. Finally, this year, I broke 5:00, and it was awesome. The strange thing is, I did not do ANY speed work leading up to this, other than one track workout nine days before. I believe that my training the last two years has led me to be able to do this - and, of course, I have done a lot of mileage the last two years, with two (and a half) more marathon training cycles under my belt. And my marathoning cycles, during which I ran anywhere from 70-100 miles per week, consisted of weekly long runs, a tempo at least every other week, a few marathon pace runs, and even a couple track workouts (but those weren't particularly fast, and they were months before this time trial). I went into this 1600 with the goal of breaking my 5:06 PR but wasn't expecting to due to the lack of training for it. Ran splits of 75.9, 76.3, 74.3, and 71.0 - 4:57.51, or roughly 4:59.3 for the full mile. I was absolutely flabbergasted that I was able to do that on one track workout, but it was just a testament to what running high mileage can do for you.
Anyway, So I don't know what you can take out of that, since you obviously aren't going to run 70-100 mile weeks training for marathons. But my point was, I think strength is important in focusing on the mile. So you can do that in whatever way you can. Obviously if you have an experienced coach (I really don't know anything about shorter distance training) that would be best, but if you just run a bunch of 200/400 repeat sessions, as well as tempos, you would be fine. Fartleks are fun too, and another poster suggested them. Good luck!