Actually still pretty simple - In almost all scenarios, the USB connections on the PC will be oriented to point downwards or to the right. You tell what's 'down' on your USB cord by looking for the seam on the outside metal band that runs around the USB connector itself.

Orient that seam downwards or (if the ports are vertical) to the right, and most of the time it'll fit first go.

I have come across a few setups that had a USB port 'upside down', but mostly this is on laptops where they've got the connector board fitted upside-down inside the chassis.