I haven't had problems shipping internationally--so however you pack them safe for transit in your country should be fine for international orders, but you should be sure to include in the package a document stating the purchase price, and include your address & the buyer's address, in addition to including a customs form. When it's a painting that you'll be shipping, be sure to mark it fine art as many countries exempt it from duty.
It's hard to say what method would work for you as I'm in the US--maybe there's someone else who can help with that. :)
(You might want to check out the "WRITING TITLES, DESCRIPTIONS & SEO" section of this blog post about writing descriptions of items in your shop to help with sales:
http://etsymentors.blogspot.com/p/critique-your-own-shop.html )
