Color coding your cabling is a great idea that has helped me in the past. Sometimes I've just been the remote pair of hands for someone, and other times I've been the person troubleshooting. It is very helpful to be able to use "the red cable should be in port X, the yellow cable should be in port Y, and the blue cable should be in port Z". Also make sure any diagrams left at the site use the same colors.
Don't be afraid to have another set of eyes review your configs and scripts. It is too easy to see a configuration that is in your head but not really in the running config or the script that is about to be the running config.
Don't change configs until after your morning coffee, smoke, Dew, whatever.