Carry tweezers with you. You wouldn't believe how many times when the ATM tried to return our bank card, only a few millimeters stuck out, which made it impossible to grasp with our fingers. If you are unable to grab your bank card, it will suck your card back in and you'll have to see if the branch is able to retrieve it for you if you show your passport. Bringing a backup card is handy.
We've come across a couple of food writers/bloggers, Elizabeth Minchilli and Katie Parla, that we're using for ideas on where to eat. Elizabeth Minchilli has a couple of city guide food apps too for a few dollars.
Make sure you validate your train ticket before you board your train. They occasionally bottleneck to a gate when you get off to check tickets and fine you on the spot w/out a validated ticket.
Many museums and sites have tricks to skip the line: Making reservations/booking ahead, buying a dual purpose ticket as the less busy place, etc. Personally, I like the Rick Steves guide books for Europe which list most of these tips.
I like to buy a day pass and cruise the canals of Venice on the Vaporetti.
Read up on the potential scams. When my sister when to Europe for the first time a few years back, we chatted about all the big and small scams so that she would be able to recognize potential situations: mother with a baby, herds of kids surrounding you, found ring on the ground, ketchup on your clothes, bottleneck at the end of an escalator, grab n dash via a scooter or off the metro, no pricing for an can of coke or a scoop of gelato (always ask)... the list goes on and on.
Italian trains seem to be always late. Don't count on them to be on time.
Labour stoppages/strikes are common in Europe/Italy but they're typically announced ahead of time so people can plan around them. You can google for
sites that show a list of upcoming events.