When traveling to Italy, everyone wants to know some basic information to make the trip pleasant. Where is a good hotel, what forms of payment are accepted in shops, how to mail packages and postcards, etc.
I find TripAdvisor very helpful with hotels in towns I have not visited before. If any of you would like my recommendations for hotels in Italy, just ask.
As far as money goes, cash is king. If you pay for purchases in cash, most places will give you the VAT (Value Added Tax) on the spot without any paperwork. Sometimes a little extra discount is added also. The ATMs are plentiful, but be aware that some bank ATMs may not accept your credit card. I always advise people to bring several. Checking with your bank at home before you arrive, you may find that they partner with an Italian bank, and you will not have to pay a foreign transaction fee. Some credit cards do not charge a foreign transaction fee at all.
All of the stores will accept major credit cards, but they prefer not to use American Express if possible. 
As of September 1, you will need to show your passport in the stores to obtain the VAT refund. If you reside outside the EU, you are entitled to this refund which is around 12% of the purchase price. Taking a clear photo of your passport on your smart phone will work also.
When you have had a major shopping spree, you may want to ship purchases back home. Shipping packages from Italy is expensive. Sometimes a store will offer to ship for free, but not often. For example, a handbag costs about 45 euro to ship from Italy to the USA through FedEx insured. If you intend to ship via the post office, always ask for la recivuta di ritorno e per confermare. I shipped once without this and the package disappeared!
Postcards abound here and there are lots of beautiful ones. But trying to buy the stamps is a big headache! I just purchased a few postcard stamps and it took me 45 minutes at the post office. If you are coming to Italy and want to send postcards home, contact me and I will send some to you before you leave. There are way more fun things to do here than sit in the post office!