We've found that the best approach is to stack your Media in a sturdy cardboard box so they have little to no room to move whilst in transit. It's also a good idea to fill any remaining spaces with bubble wrap or newspaper for that extra protection.
This is also a good time to check that your Media contains the original artwork and that the cases have the discs inside.
It's important that you remove any old barcodes/labels from any reused boxes as this could cause delays in the carrier network.