I recently received a guitar that came to me in a shipping box with no padding in it whatsoever. I gingerly pulled the case out, noting that fortunately it was a very good quality hardshell model and there was no obvious damage. I put the case down on the couch, took a deep breath and opened the latches. Relief! The guitar fit in the case perfectly and the case had done its job. No problems, thank goodness!
But in spite of my good fortune - or rather the former owner's good fortune because if there had been damage he would have received that guitar back with a demand of a refund - it was a bit depressing to realize the previous owner's either neglect or ignorance of proper packing, or both.
I won't bore you with stories of broken guitars I've seen due to shipping mishaps. I'll just get right to what proper packing is all about. Let's say you need to ship your guitar. The first thing you'll need is an appropriate shipping carton. These can sometimes be had for free or for a small cost at the local music store. You can also order new boxes from the huge shipping container company Uline, but you'll have to buy a half dozen at a time and they cost about $9 each, plus the cost of shipping them from Uline. If you go that route be sure to order the LARGER version of the two that are available, as that one is designed for acoustic guitars and cases.
The first step is preparing the guitar for maximum protection inside its case. Of course we're assuming you have a decent quality, hard sided or hard foam case, not a gig bag. Although I know some of the big online retailers do ship guitars in gig bags I would never be comfortable with that. It you must do it, spend extra time with padding all around the guitar and even perhaps and extra layer of cardboard to stiffen up the box.
The crucial support point are the upper neck/head and the bottom of the instrument. Those are the areas that must absorb or deflect the force of the box being dropped on its ends, which I suspect is all too common in Fedex and UPS shipping facilities. Carefully wrap the head and upper neck with plastic bubble wrap, endeavoring to fill the entire cavity in that area of the case. If the guitar has a strap button on the bottom, remove it if possible. That can be a severe stress point during a drop. If you can't remove it, place some more bubble wrap down there between the bottom of the guitar and the inside bottom of the case, if possible.
There is controversy about whether to ship a guitar tuned up to pitch or tuned down. Martin says you should ship with the guitar tuned up because that "stiffens" the entire instrument, making it stronger. I'm not comfortable with that line of reasoning, although I realize they ship way more guitars than I do! I still tune the strings down quite a bit, but not all the way because I feel that removing all the string pressure from the neck and then reapplying it when the guitar is tuned is not a good thing. I think the neck just has to deal with too much variation in stress doing that.
Now the really crucial part: what goes in the box with the guitar in its case. Many people opt for those super annoying plastic peanuts, which work pretty well but be sure to check with your carrier about the use of these things. Some companies are not in favor of their use and using them may in fact negate a claim you would have against a shipping company for a broken guitar.
Some companies use neat little folded and shaped pieces of cardboard that support and hold stationary both the top and bottom of the guitar. I like those things and always use them if I have them from a guitar that has been previously shipped to me. Keeping the guitar stationary is essential for safe shipment. Then it's a matter of filling in the voids. I often use those annoying peanuts for this, or broken up pieces of styrofoam or if nothing else is available, loosely crumpled newspaper.
Then securely tape the top and bottom of the box, remove all labels and cross out any addresses if the box has been used before, and be sure to apply "fragile!" stickers on all sides. You can buy these at an office supply store, or go to Google Images, type in "fragile" and you'll find many you can print and tape on.
I'm knocking on wood (no pun intended!) when I say this, but up until now I've never had a guitar I've shipped arrive damaged. In some cases the box was thoroughly beat up and dinged, but that's the way it goes.
Most of all, don't rush through the packing process. Think things out, take your time and do it right. No guitar deserves to be broken due to simple neglect.
Peace & good music,