Protect the quiet zone
Leave a blank margin around the code. A border or caption belongs outside that margin. Do not let a design editor crop it.
Size the code for its use
A close-up label and a lobby sign need different sizes. More embedded data creates smaller modules at the same physical size. Use a short URL when you can.
Test the real scenario
Scan the exported code, then the printed result. Repeat the test at the expected distance and in similar lighting.