Wiring is so important, not just to look good but to be able to work around it without catching wires with your fingers or tools. Good wiring will not come apart at the worst time during a match (except PWM cables). And good wiring will make it easier to troubleshoot and replace faulty components.
Wireties' list is great and includes almost all the things I would have mentioned. As a controls engineer who spent many years wiring I like to think of the robot as a training ground. As you can see from this thread there are many things to know and tricks that help. I usually do a lot of talking while the students are wiring, hopefully helping them learn.
We plan ahead using AutoCAD Electrical to make a full schematic in the style most used by automation manufacturers and label our wires according to the line they are found on the schematic, and try to make sure the people wiring understand what all components are doing.
Here is our schematic from 2010 (if the link works):
http://www.chiefdelphi.com/media/papers/2384