Personally I think the two main areas where your speed is developed is on the field and in the weight room. But you can be training completely wrong in both areas and not get any faster.
In the weight room you need to be working explosive movements in a low range of reps focused on being as explosive as possible. 1-5 reps in my opinion. Some of the better exercises for this are squats, power cleans, and overall plyometrics. Which includes box jumps or any kind of jump training where you must be explosive and generate force. The wrong way to workout for speed is to do slow movements in a high rep range. The high rep range is working your slow twitch fibers which helps with your distance running. Not speed. If you are a cross country athlete thats what you want to be doing.
Now on the field, I always recommend resistance work. So band work, sled work and hill work are all great for your speed. Same thing as the weight room, I wouldn’t suggest doing 100 sprints, I would suggest doing like 10-20 but focus on being as explosive as possible taking enough rest in between each rep. Don’t run for distance. You can do that for cardio but that will not help your speed at all. It’s not helping your fast twitch fibers, again it will be working the slower twitch ones. Train for what you want to improve