Since QR Codes are Fragile, here are a few things to note that are discussed in the video:

The code needs to be readable as a square, so you cannot stretch it in any way unevenly.

The code must have the same URL at all times, so a website that changes its link will break the code.

 

One thing not discussed is to keep your QR code readable when applying colors.  Avoid mixing light and dark colors so the phone can read it as a QR code.  The closer it is to black and white, the better!