How can I jump farther in long jump?

During my freshman year the best that I could do was 15ft 11 1/2 inches. Right now it's summer and I will be a sophomore. I have been working hard for the 400 meter dash. I checked how far I could jump yesterday and even though my foot wasn't on the board, my dad measured from where I had jumped to where I landed. I got 16ft 8 inches! But I really want to impress my coach at the start of track season so I want to be able to jump something like 19 ft. Does anyone know what I should do to increase my distance? Please give me something I can actually do, not something stupid like "hit the gym"