Other than what ArchtopAnimal noted above, a regular flat top acoustic/semi hollow/hollow etc should be perfectly safe if it's shipped in a good quality hard case. Also, a manufacturers original box (for fit) is always good to use if available. If you're really concerned, buy a larger box and fill the bottom (maybe 2" worth ) of packing peanuts, place the guitar case in the box and then surround the case with the same packing material.
When I ship any guitar, I always make sure I tape closed any and all seams, to prevent ( as much as possible) any water getting in. This also prevents loose corners from catching on something and the box top/bottom ripping open.
Other than that, you keep your fingers crossed. If they're going to drop something heavy on it, no matter what you do, you wont prevent damage. On the brighter side, think of how many manufacturers ship guitars every day of the week. The y cant afford to loose guitars to mishandling and FedEx/Ups/DHL etc cant afford to be paying claims. I'd say you'll be fine if you follow the above steps.
I have shipped over 100 guitars and I have never had a single complaint or problem.
I hope this helps
