This plan is a progressive flat work plan. Start by walking large around the whole school and on the long sides ride a counter bend and then make a smooth transition back to true bend maintaining a even rein contact. Do not be in a hurry when you change for one positioning to the other and really ensure that you are maintaining a correct position and aiding to the left and right. Make sure you are controlling the hind quarters and ensuring the horse does not over bend in the neck but a maintains a uniform and equal bend in front of and behind the saddle. Repeat in walk on both reins.
You can then progress this to riding a leg yield along the wall on the long side in walk, a smooth change of bend then a transition to trot. You want to progressively develop your feel through the change of bend and the transition to feel that key moment when the horse is even in the contact and beautifully straight to make the transition. You can then add a 15m circle in at A and C in trot. Ensure that you downward transitions to walk and well prepared and balanced towards the hind leg legs.
You can then when you feel ready (not necessarily in one session) progress to riding the leg yield along the walk in trot and then change the bend and ride a transition to canter and a 15m circle at A and C. You will have to make sure you maintain an even rhythm in the trot and again straighten the horse between you legs before you canter.
The last addition is to add in circles at E and B also so you make them more frequently. Between each circle you ride the leg yield then straighten the horse into an upward transition, circle, downward transition and leg yield again. You can make in harder again making direct transitions walk-canter, canter-walk.
If you have any problems with this exercice please email me at firstname.lastname@example.org , I would love to see some video too!