Mark your cables to make it easy to put them in the right way.
One of the downsides of an iMac is that there is never enough USB ports. I am constantly switching thumb drives or printer cables to the back of the computer.
Ports on the Back of an iMac 2011
One thing that annoyed me is that I never put the cable in right. I am always putting it in wrong and having to flip it over to get it in right.
A quick solution that I came up with is to mark the top of the cable with a white Sharpie China Marker.
Cables are marked.
So now when I need to put in a new cable, I just look for the white part and know that it will go right in.
You can use any white marker to label the cables. I just happen to have the white China marker at my desk. It's nice because it's not a permanent solution and I can remove it when needed.