Simular, or maybe even the same as Scotts example, I use simple line diagrams.
And, there is a standardized methods outlined in several books.
One step further from the above example is that for easy referance of conduit vs cable is to put a small cicle on the line ane call out the size near it for conduit. (no circle for cable)
Also add hash marks on the line for conductor count, grouped in circuit bundles. And add designations above the line,and hashes. or skip the hashes all together.
Example:
(10)A,B,C,N - (12)S,T,A,N
(this would be one round-house, one switch wire, a set of travellers, and phase A, and a neutral) 9 wires, althought you may want to use a few less.
And/or the other information Scott mentioned below can be broken down into a code simular to what the phone companies use for cable administration.
for the same example above: Add Panel LP-1, and CB numbers, and Fixture 9.
LP-1(10)2,4,6,N-(12){F9}S,T,8,N
I have to do this for some of the installs I do network cabling for. Problem is that different companies I do work for have different codes, so I have to follow thiers, most are pretty simular though.
http://web.anixter.com/anixter/anixter.nsf/StandardsGuides/WiringSystemAdministration
