pessoa lunging system is a great tool to teach the horse how to carry themselves and use their bodies.
Stretch them forward and down for a couple years is the 1. Way but people are too damn lazy
Pessoa on the lunge, raised trotting poles, hill work
Direct transition (trot to stand, stand to trot/canter), pole work and cavaletti, grid work and riding uphill to encourage and build topline and hind quarters.
Lungeing in a passoa for topline and add to it some poles and cavaletti.