Cup the horse's chin in one hand, then place the other hand on the horse's forehead, and just be there, breathing with the horse.
Place a hand flat on jaw, neck, shoulder, side or haunch, and feel the horse, and breathe with the horse.
When mounted, sit quietly for a moment. Feel yourself sinking into the horse, and your four feet placed on the ground. Breathe into the horse.
Now move, together.