NagaBaba

You need a systematical preparation of your body for high flying break falls.
First step is to learn the correct shape of the body when you land. To do it, you can start with a simple roll forward, but this roll you finish slapping tatami with all you power with one hand and your knees wide open. The feet should touch the tatami in the end of the roll gently. In this form of ukemi, in the end, you don't get up, but stay flat on the tatmi. Only one shoulder and feet should be in contact with tatami.To do it, push your hips up.

Second step Marc described correctly, only when you land, you have to apply the shape of body you learned in previous step. This step you must repeat until your body is conditioned and you have no fear at all. Body inside you must become very soft to redirect as much impact as possible with flexibility.This must be practice EVERY time you are in the dojo 500 times minimum.

Third step is to do break falls by somebody who stands but has his upper body 90 degree to his legs. In this exercise you use everything you learned previously. First you start very statically, lift yourself over your partner body with your hands and go down the other side with your head as close as possible to the tatami.
After the while you can learn how to use your legs to jump over his body.

I know it is not very clear, but it should only give you a general idea. You instructor should have a system to teach high flying break falls...