Hi,
Most important is probably writting the destination in large and standard letters using all available space and also clearly writing a return address somewhere. Also keep in mind the language of the mailman/woman delivering the parcel. They can not always understand what is written obn the box in the senders language, English is mostly no problem but French, Dutch, German, Italian, Spanish etc, everything comes by in a weeks time.
The ZIP codes here are extremly easy. Every number in every street in every place can be addressed simply by ZIP code and house number. In Holland, if you mail something to us, 3067DC 36, would be all that is necessary:
30 Stands for Rotterdam
67 Stands for the neighbourhood
DC Stands for the row of houses
36 is our house number
Thats all.
For US mail I always write the State in full as I do not know if the mail is sorted out here and send to for instance LA, NY etc. Or if all is send to one city in the U.S. and sorted out there. When things are sorted out here I would not want them to mistake Wisconsin (Wi) for Wyoming, although an easy difference for someone who knows this in the U.S. it might be confusing for a non-US postal worker and put on the wrong plance, making delivery time so much longer.
Another tip, from experience, is for U.S. seller who ship to Holland/The Netherlands PLEASE use The Netherlands as it has happened several times now that USPS send parcels with HOLLAND on it to POLAND lookig at the postal stamps on the boxes and the very long delivery time. For Dutch buyers, please use The Netherlands for international transactions outside Europe, it can make your life easier.
An anekdote is that we were once stopped by the police while taking photos in the U.S. and the Southern Police officer said, with his accent, to the californian radio room employee "These people taking photos are from Hooland", which was changed to Poland in the radio room and before we knew it we were waiting in a room for the FBI to show up several hours later from Sacramento. WHen they saw our pasports all was OK again and we could leave after having a laugh and a coke with them. The police officers face was
Dennis