Mind-map your studio i/o
Here's a tip from Devin Townsend: use a mind-mapping tool to document all the i/o in your studio.
If your audio interface only has a couple inputs, this sort of thing would be unnecessary. But as you accumulate more gear -- a larger interface, ADAT expansion, external mic pre's, etc -- it's incredibly beneficial to map it all.
This map was made with a tool called Coggle. The free version of the app is adequate for a basic map/diagram like this.