for strength/explosiveness i would ask coolcolj has he seems to be the resident expert, but i would advocate sprints 2-3x a week while "bulking" and explosive movements and plyometrics, box squats, high rep squats, shorter rest periods , and probably some more olympic lifts (which i really have no knowledge on). What i used to do during the off season was sprints eod, and plyometrics on days where i wasnt sprinting all out. Now, ill probably catch shit for saying this, but since i was more interested in short bursts and not really concerned with size while running track, i used to do 2 sets of squats to mimic the jumping motion, meaning i would cut the weight down, go deep as possible, then explode up onto my toes and hold it there for a few seconds, then back down. Try doing 15-20 reps of those!! I would then do 3 sets of 3 heavy squats.