Depending on the size and weight of the package you will need to decide for yourself which carrier is best to handle your items, the general options are UPSP, UPS, and FedEx. Best to start shipping internationally with a few cherry picked countries, where you can easily access their custom's law and exact shipping rates, rather than jumping in with both feet to ship "everywhere else". Do this till you feel comfortable with filling out all required international paperwork and develop a customer positive yet firm international shipping and return policy (that is posted in your shop).
Each carrier company has it's ups and downs. Like for smaller light packages USPS is great because their First Class International is affordable, but it does lack tracking features once a package leaves US customs. UPS and Fedex can track all their packages directly to their general destination, but in most countries the customer will need to pay a brokerage fee (in additon to their country's tariffs or import taxes) directly to the delivery person before being allowed to claim their item. For heavy packages (like over 3 lbs.) UPS is a better cost choice, than say USPS, but they may have restricted delivery in certain countries and require the customer to show up at a central processing office to claim their package. While USPS works directly with whatever mail system the other country has and will deliver a package directly to the address (as long as delivery is offered there), but it can cost double without the assurances of tracking or insurance that can be had from UPS or FedEx. Also make sure you understand how to properly address the package, some countries require a slightly different format than what we are used to.
Hand pick 3 or 4 countries your willing to ship internationally to start, ETSY allows you to pick specific countries instead of shipping worldwide. Not only will this allow you to offer pin pointed shipping rates, but it gives you a chance to see how other countries handle your delivery and if you're comfortable with the laws of shipping overseas. All countries have laws about what can be shipped into their homeland and the aurthority to confiscate or destroy products the see as unfit for their population or as too competative to their own markets. Italy is notorious about not allowing fashion items and accessories to be shipped in from overseas without a importer's license and many package become mysteriously lost once it enter Italian customs. Then there are religiously controlled countries that can decide if a product is subversive causing the package to disappear. While other countries may need additional paperwork to prove the item is up to their current product laws or it's returned to sender at the sender's expense, like EU trade agreement countries require safety documents for any children's products. It's best to research the customs laws for each country you're willing to ship to to head off problems in advance, so start with a few where you can access their shipping regulations.
Also you will need to protect yourself from ignorance and out-n-out scams. International packages shipped at an affordable rate can take a long time to arrive, I've personally had 1 item take 4 months to clear German customs, and PayPal still only allows the customer 45 days to open a dispute. This discrepancy can force a seller to offer a refund or replacement while the original package is still in transit. Package tracking or insurance (and tracking/insurance add a hefty cost to shipping) can offset these claims but it will still take the seller time to sort out the dispute with PP and the customer. One of the most common scams to avoid is the customer requesting the package being sent as a gift or some other non-tariffed catagory of mail. This can lead to you being fined by the US government for mail fraud, if money exchanged hands between a seller and customer for the item to be shipped it's considered a commerical good and must be sent that way. The best way to avoid these requests is to already have in your store's policy that tariffs and national taxes due to the sending country is the buyer's responsibility and may be require payment to their government before the package is released. Also there may be brokerage fees due to the shipping carrier that can not be predicted before the package arrives that should be paid by the customer direct to the delivery company.
So investigate various shipping carriers to see what works best for your product. Check out customs and import laws and regulations (start w/ each country's restriction pages from the carrier you decide on) to decide on a few countries to start shipping internetionally to. Develop a seperate shipping and return policy for international orders. Package shipments very thoroughly to protect from damage including a secondary address label directly on the product if the mailer and item get seperated. Make sure you understand which customs forms are needed and how to properly fill it out for your products. Remember PayPal takes a money exchange fee on foreign currancy so figure that in as part of your shipping fee.
Best of luck.
