Something I learned a few weeks ago (after many years of using USB) is that usually cables have the USB logo or marking on the "right side" up. So if you don't know which one is the right side up, the one with the logo should win.
Same with my monitor! I've found that what would be the natural axis towards you usually work, at least both on my TV, desktop computer (because of course you have the chassi on the right) and monitor.
i know it's a joke, but the usb logo on the plug is always on top, so you can just orient it 'up' according to the underlying board (up for laptops, and facing left for desktops)
The side of your case that has the motherboard's backplate (where you plug everything in) is the bottom. On the vast majority of towers, the plate is on the right side, meaning left is up.
EDIT: right/left when looking at the front of the case.
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