Put the original packaging inside a bigger box. Make sure the item is protected inside from all sides by chocking sponges between the surfaces.
Check if the item stays stable inside the packaging layer in order to avoid damage during transport. If not, add more protective materials.
Please take note that the use of carton box and sponges is mandatory for the safety of the package during delivery.
Gather all relevant documents such as invoice, warranty certificate, instruction manuals, and accessories and make sure these are complete.
Use a strong packaging tape to secure the box.
Last but not the least, stick prominently the printed Seller Center airway bill on the parcel before releasing the package to partner 3PL or Third-Party Logistics