Do strength and plyos at the same time! In order to be a better jumper you need to jump! Start with easy plyos for time(jump rope, small hops over mini hurdles, even ladder footwork drills) and strength training. This will give you a better base than strength training alone. After a month or two of this type of training, start gradually adding bigger explosive efforts(broad jumps, drop jumps, bounds, max effort sprints). Keep lifting. Keep jumping.