Only address one side of the package. Postal workers are on deadlines and must work quickly. If a worker picks up a package to sort to the correct bins and happens to pick up a side with the address but no postage because it is attached to the opposite side. They may assume the parcel has no postage and put it in Return for Postage bin which delays it. But do use the packing tape on the address and put the destination on the inside, too. Then when it ends up in the Dead Parcel dept. and they open it, they will be able to rewrap and put a new address label on it.