When I first began selling art on the internet in 2005 I was a novice. Hundreds of packages later I think I might qualify as an expert. I stock bubble wrap in rolls, have had to install shelving in my garage to store shipping cartons, and I can estimate the weight of any package under ten pounds pretty accurately by just lifting it.
Many of my recent sales have been international. I've sold three to clients in Japan just this month, when I typically will have 4-5 international sales per year. If you're going to ship art out of the United States you need to know that each country has its own specific rules regarding imports. Some countries charge an additional tax on foreign goods and the buyer should be aware of this. YOU need to be aware of this too in case they question you about it later.
The U.S. Post Office has a lot of information about shipping internationally on their website here.
(see link here) if you use their Priority Mail service. I highly recommend using them for most international shipments, as they are less expensive than FedEx and UPS. I don't ship larger paintings overseas so this may not be true if you are mailing a heavy frame or a bigger piece. I limit my international shipments to anything I can fit into an 18" x 24" x 4" box, because I stock that box size and it's the largest size you can ship before the price escalates.
International shipping with the USPS requires the use of a shipping envelope for your customs forms, Form 2976E, which can also be acquired for free from the USPS. Print your customs forms on line at the USPS site or using Paypal. You will get four copies. Cut the sheet in half, sign three of the copies and keep the fourth.
link to a page where you can print a PayPal label through Pitney-Bowes for any package if you have a PayPal account. It's nice because you don't share any credit card information and it costs you nothing.
You can't schedule a normal mail pick up for International shipments as I routinely do for U.S. Priority Mail shipments. You have to hand the package directly to a postal worker, so it usually requires an additional trip to the post office. But I think the benefits of shipping to other countries outweigh the few additional steps you have to make in the shipping process. Who knows-- maybe your work will become highly sought after in another country and they'll invite you over to give a seminar. We can hope! :)