I would like to add that proper clothing sometimes matters a lot, especially for some italians.
Please avoid taking off your shirt if you are not on the beach or in a park. Avoid sleeveless shirts and hotpants while visiting churches and museums.
Touching children isn't usually a taboo, but taking a picture of them can be a problem with some people, so it can be a good idea to ask before.
If you are invited to someone's house it is always a good thought to bring something (a bottle of wine, something sweet, a small gift and so on).
If you eat in a restaurant, and you like the food, feel free to tell it to the waiter: they usually like when the costumer show appreciation for their work.
And tips giving is not the same everywhere, but usually we give it just if we did love how the waiter/barman treated us (so feel free not to give it, it is not impolite at all).
Be careful when you need to pay with credit card, because some places don't accept it unless you reach a minimum amount (often 20 euro).
For the moment I can't think of anything more.
Have fun in Italy!!