點樣先可以跳高啲

speed is very very important
High jump is a game that transform the horizontal speed into vertical power(by a pivot mechanism). so the faster you run, the higher you jump.
However, your must have enough skill and power of you jumping leg to control the speed, otherwise you will just jumping forward rather than jumping upward.
So high jump actually is not just use your jumping leg to jump with its own power.

How to transform the horizontal speed into vertical power?
The last three strides is extremely important. During the last 3 strides, the time and distance between each stride will be shorter and shorter ( especially in the last stride)
During the last stride, you whole body should lean backward straightly, and facing 30 degree toward the bar ( remember that you should not parallel to the bar during jumping). step on your whole feet on the ground ( not using the heel). Your jumping leg act as the pivot point. Than use the another leg (not the jumping leg) swing up and inward, so that will produce a upward and rotational force, that will make you fly up and your face will opposite to the bar. Then you can continue with your flopping over the bar.

There are many biomechanical theories you need to learn for high jump. Not only the take off, but also during the flopping over the bar. If you are interest, you can read some books about athletics/high jump.

When I was young and as a high jumper, I read many books on the theories and that help me a lot.

跳高助跑唔係太重要 最緊要係你要成日practic and 最後既 leg 要大prower