People are always asking me how to pack a guitar. The three biggest mistakes that most people make are:
Make sure the Tremolo Bar is securely wrapped up in a small amount of bubble pack or newspaper. If you don't do this the tremolo bar will fall out of the compartment during shipping and scrape up your guitar. Also it's a good idea to make sure there are no tools or itsy bitsy screws anywhere in the case.
DO NOT LOOSEN ALL THE STRINGS!!! This is always a major hassle. I get an average of 5 used guitars shipped to me daily. It is a lot easier for me to check the guitar out if I don't have to do a setup first. By loosening the strings as much as people do they usually blow the setup. Sometimes even bridge saddles fall out and cause damage to the guitar. Gibson, Fender, PRS, Hamer, Ibanez, Heritage, Washburn, Ibanez, Jackson and all the other companies ship guitars to me perfectly in tune right out of the case. Vintage guitar dealers and other trunk gypsy types always loosen the strings. This way they can get out of doing a setup on the guitar before they ship it to you.
DO NOT TRUST LOOSE STYROFOAM SHIPPING BEANS/PEANUTS. Loose Styrofoam beans are useless for shipping anything delicate. They always settle to the bottom and basically offer very little protection against anything. Bubble pack is the best bet. Even wadded up newspaper is better than beans.
Shipping a guitar is easy as long as you use common sense and a lot of bubble pack.
It's good to make sure the guitar cannot move inside the case. Usually a little bubble pack at the headstock area will solve any movement problems.
Make sure the case does not flop around inside the shipping box. That will cause a real lot of damage.
If you are shipping a guitar without a case (No Problem) just MAKE SURE you use a lot of Bubble pack taped securely around the instrument. 3 layers at least and maybe a little cardboard in between the layers on sharp corners or at the headstock.
Usually most music stores have boxes they are throwing out or have to get rid of, so that's a good place to go get a box. I always advise my customers to always keep a couple of good boxes around for when they need to ship something. With all the no personality superstores opening up all over, shipping guitars will become a required way of life for anyone who wants to own any guitar that may be even slightly out of the norm.
Always insure the guitar for more than it's worth in case it gets broken or lost. Be careful because UPS and FedEx won't pay claims when they deem the guitar was packed incorrectly, so make sure you use plenty of bubble pack.