Thoroughly coat everything inside the caliper with anti-seize. Not grease, anti-seize. The caliper body, the sliders, the piston, the works. Then reinstall the pads and spring.

IME corrosion on the sliders causes the pads to stick and not retract, thus causing the brake to drag. The pads also corrode to the piston, which makes them hard to change. An ounce of prevention...