You need to buy a shock-resistant flight case if the guitar goes with the luggage (Flight case = aluminum structure + foam inside to absorb shocks.)
If you do not have a flight case:
You have a case or you have a gig bag, put bubble wrap around the case/gig bag, put in the bottom of a good cardboard box with more bubble wrap, insert the case/gig bag in the box, put more bubble wrap on top of the case/gig bag.