It is very important that the bottle or bottles are properly packed up. Preferably, you should use bubble wrap and foam flakes. In addition, use multiple layers of cardboard, for example a box in a box. Make sure the bottles cannot touch each other. Most protection materials are light and do not lead to extra shipping costs. They can prevent a lot of trouble though.
Labeling the package:
Print out the address and stick it to the box. Make sure the label is properly attached. Using multiple address labels is also an option.
The package must be sent through registered mail. You will receive a receipt from the shipping company.
Packages that are sent through registered mail are usually insured. Check for conditions with your shipping company. If a package is lost or damaged and needs to be claimed, you will need the shipping receipt and a purchase receipt or sales order. Often pictures of the damaged object and packaging are also required. If the bottle is not properly packed up, the claim may be refused. Reimbursement varies from shipping company to shipping company. Sometimes the purchase value is reimbursed, sometimes the sales value. The claim will also be refused if the package is shipped to a country that does not allow shipping of whisky.
Some example images from an excellent way of packaging (bottle&box separated, plenty of bubble wrap etc...)