This is Eugene posting. First non-uenao post?
Although I can jump a fair bit of distance, it isn't really an achievement... because we measure progress by comparing it with what you can do in the past (maybe last year's NAPFA for good reference).
In that case I am doing just slightly more than last year.
I don't have any sure tips of jumping further, but anyway, some things to take note:
1) You have an advantage if you have long legs. Duh.
2) Look forward while jumping, don't jump while looking at the mat. Look after you have jumped.
3) Angle of projection. It's important but I have no idea. Don't try measuring or whatever. But testing around can be it.
4) Time your swing well to help your propulsion. Swing back, forth, back and jump as you swing forth.
5) Practise a few times of jump everyday.
These are just general ideas.
Whether it works or not, I cannot guarantee. But you should judge progress rather than what grade you get. Yeah.