Unlike barcode scanning in retail locations that uses a laser, using a camera to scan requires good lighting and contrast in order to read the code. Try these tips to help increase scanning success.
Hold the QR code about 2 to 6 inches away from the camera. Smaller codes may need to be closer than larger codes.
Tilt the QR code so it's square in the camera preview and not skewed.
Try to illuminate the QR code by making sure your room's ambient light is shining on the QR code. However, if QR code is printed on glossy paper, you may need to tilt the code slightly to remove the reflection.
If you are in a low light area, try adjusting Camera Contrast under Preferences.