If the push-rod is free to move, for instance if it's a long piece of balsa rod, then the rod should be arranged so that it's perpendicular to the hinge line. At neutral the rod should also be perpendicular to the servo arm  and should be parallel to the chord line of the control surface. The shape and rake of the control horn don't matter, what matters is that the attachment point of the rod to the horn is perpendicularly "below" the hinge line of the control surface. This will give equal throws and remove the tendency for the control rod to rip off the horn.

If you're using Bowden cables or "Gold'n rod", then the cable needs to be attached to the servo so that at neutral it's at 90 degrees to the servo horn. At the surface, the cable needs to be perpendicular to the hinge line and parallel to the chord line for best effect.</p>