Mostly I move around regularly on longer climbs, engaging slightly different muscle groups....let them all share the agony. Like others above, hands loosely on top sits me upright to improve diaphragm breathing but puts more stress on the quads-- eventually reducing the spin to that more piston like pedaling that tells us we've hit whatever our level of conditioning is calling steep. Even a slight movement or angle change can refresh you. When you run out of positions and start switching too frequently and to no effect, then you know the work has really begun.