1) Make sure that the tab on the pad is lined up correctly in the caliper. Otherwise you will get uneven wear and screeching prematurely.

2) Make sure you grease the back of the pads. ALWAYS.

3) Make sure the pins move freely when you reinstall the caliper.

The dust shield could bend and cut the rotor, you should be able to diagnose that by lifting the car and spinning the wheel. If you hear "whoosh whoosh whoosh" as the wheel is turning from a light scraping, there is some contact.