Before we get into the things you must do to become a better athlete before next season, let's start with some important distinctions. Speedwork is different from conditioning. Speedwork develops exactly that—speed, the ability to move from point A to point B as quickly as possible.
Conditioning refers to the ability to move without getting winded.
Speed is strength—you need to be strong to move fast. But there are three different kinds of strength: absolute strength, the ability to lift a really heavy object; speed strength, the ability to move a weight as fast as possible; and repetitive strength, the ability to perform a movement over and over.
Each type of strength requires a different approach for development. You build absolute strength by using sets of 3 reps or less, often going with single reps at max or near-max weight. Speed strength is built through sets of 2 to 3 reps for 6 to 8 sets with short rest intervals between sets. And repetitive strength is built by working with moderate weights and high reps (15 or more per set) for 4 to 5 sets.