When deciding to ship your guitar make sure it is protected no matter who handles it. The best protection comes from a hardshell case.
It is also recommended that you loosen your strings before packaging. This will remove tension on the neck. Throughout the journey, if your package were to fall, the headstock will less likely break due to the whiplash effect.
Next, remove all items from the case. However, all items that must be shipped with the guitar (i.e. strings, parts for installation...) should be put away in the accessories compartment.
Now you are ready to put your guitar in it's case. It is important to remove all air space and unsupported areas with crushed paper. The most important area being the headstock. Place the paper underneath, over and around the headstock. The next important areas are behind the neck, under the heel block and inside the waist area. The whole idea is to keep the guitar from shifting. Now place some folded paper between the strings and fingerboard. If your guitar contains a pickup, protect that as well. In the case of an archtop, place paper between the strings and body at the bridge.