Which way to mount the Raspberry Pi DSI display cable for the Raspberry Pi 7″ display

First, mount the Raspberry Pi on top of the display PCB on the back of the display.

On the bottom (display) PCB, the silver contacts of the cable should be at the top (facing the Raspberry Pi):

On the Raspberry Pi, the silver contacts should face towards the USB connectors:

Overall, it should look like this: