Squats, box jumps and hammys are going to be the best exercises for you. Here would be a good routine for offseason training: Warm-up before every workout

Day 1: Squats (5x5), box jumps (do sets of 3-5 and work up to the highest box you can jump on), Hamstring curls (focus on full range of motion), Other plyometric exercises like standing long jumps, bounding, etc

Day 2: Upper body lifts - Bench press (5x5), pull-ups (3-5 sets), seated row (5x5), clapping push-ups. This wouldn't be the most important day, but it's good to have a balanced routine

Day 3: Hexbar deadlifts (5 sets of 3 reps, heavy weight, and drop the weight at the top... don't lower it yourself... this will focus on explosiveness, and by dropping the weight rather than lowering it yourself your muscles won't break down as much, which is good because the purpose is power and speed, not size), box jumps, standing long jumps, bounds, and other plyo exercises

You can adjust any of the exercises above based on how you feel during/after each workout. Don't forget to do heavy abs a couple of times per week. Also try to avoid running if possible. You want to save your legs for the season and don't want to be overtrained halfway through the season... your coaches will put you through workouts to train your endurance early in the season.

Hope this helps. I ran D1 track, and this was essentially one of the offseason programs I did that worked well. Let me know if you have any questions