Guitars are extremely fragile instruments, and any sort of physical damage to the neck or body can severely alter a guitar's sound. If you are moving homes and need to pack your guitar in a moving truck, you need to take the proper steps to ensure that your instrument is adequately protected against any physical damage it may experience while in transit.
Before You Begin
You'll need acid-free packing paper, bubble wrap, painter's tape, a large cardboard box, and a marker. You can purchase all of these items at any moving or storage supply store if you do not already own them. You'll also need a guitar case that fits your guitar, which can be purchased at most musical supply stores if for some reason your guitar didn't come with one.
Packing a Guitar
First things first, you'll want to loosen the strings of your guitar. Don't remove them completely, as they can be a real hassle to put back on, but you want to make sure that they are slightly slack to reduce the amount of stress placed on the bridge and neck.
Then, put the guitar into its case. You'll want to line the case with packing paper to ensure that the guitar is snugly fitted into the case: if you can shake the case and feel the guitar moving around, you need to add more paper to the interior to hold it in place. This greatly reduces the risk of the guitar shifting and becoming dented or damaged while in transit.
Next, you'll want to wrap the entire guitar case with bubble wrap. This provides a secondary cushioning layer that will keep your guitar in good condition even in the event that another object falls on the box or case.
Then, you'll want to slide the bubble-wrapped case into the cardboard box. Just like the interior of the case, you'll want to fill the empty space within the box with either packing paper or bubble wrap to prevent any sort of movement.
Once that's done, you can seal the box up with painter's tape and mark it fragile. Be sure to indicate that a guitar is inside as well, to speed up the unpacking process. Then, all you have to do is load the box into your moving truck (or have it done for you if you have professional movers). Just make sure that the box is wedged into a place where it won't shift around as the truck drives, and that no objects are stacked on top of it.
Check out a website like http://www.allenstransfer.com for more information and assistance.