Lunging with side reins if you do not have a lot of time at the barn. Helped my pony build up a nice top line. Hope this helps!
hills hills hills, risen poles, grid work,work on creating 3 different speeds at each gate (collection,working and extension) - depending on how green of course but even alternating between slowest possible pace you can travel at the gate and the fastest - without running! and feed plenty of fiber & protein which will promote growth.