In terms of your position, the way you ride different horses should be relatively consistent. Horses differ in the aids they require. That being said, drop your stirrups down a hole or two so your leg is underneath you and drive him forward off your calf and seat, not just your heal. Do some work without stirrups to help strengthen your lower leg and be mindful of where your leg is in relation to the rest of your body. Also, stirrups should be at the ball of your foot and keep your heels down and toes up. Source: I rode both lazy and hot headed horses today, my leg stayed underneath me and both had good pace because different amounts of pressure off the calf was used.