Great question. The best way to increase your broad jump is to practice it. The body will respond to whatever stimuli is placed on it (SAID Principle) so practice makes perfect. The second best way to increase your broad jump is to get strong particularly in the lower and core parts of your body. Squats, lunges, step ups, hip thrusts and not to mention power exercises like Olympic lifts and med ball work. The stronger and more powerful you become the better your broad jump will be. Lastly, body weight. It is said that for every pound on your body you need 4 pounds of force to overcome it. With that being said body composition is critical to power output. Losing unwanted body fat and increases lean mass will help your body overcome the inertia needed to move forward horizontally. Best of success to you.