This sounds like a simple exercise but it's a useful one to build your skills in more than one area.
To set up the exercise erect a fence at B or E on the long side of your school. One side of the fence should be up against the edge of your school. Make this fence a sensible height you and your horse are comfortable jumping out of canter.
The idea of the exercise is to start at one end of the school, say from the AF corner, assuming that your fence is at B. Canter over the fence, then come back to trot just after M so that you can then ride a half 10m circle, make a transition to canter as you head back towards the track, then jump the fence from that end. Repeat the half circle in the AF corner and then jump the fence again.
You can do this, say two or three times from each end of the school. The idea is to make good upwards and downwards transitions each time, ensure you have a good even canter stride throughout the whole exercise, popping the fence neatly each time. As you can imagine, this exercise happens pretty quickly so you need to have complete control so you can execute the transitions and the half circles exactly where you want them. It's important to think about the rhythm throughout the exercise.
An alternative is to do walk-canter and canter-walk transitions as part of the exercise.