Best way to get around the city
Rome is pretty convenient to get around. I'd recommend attempting to walk if you can! Especially during the day time as the surrounding architecture is beautiful! For longer distance, Uber black is the best way we got around. For longer Uber rides, we scheduled it in advance (example: Rome to Porto Ercole - 2h ride).
Venice isn't huge, so if you wanted to walk around, that's what most people do. You could get a day pass for water bus and explore nearby areas too. Note that water taxis are also available, but very expensive.
Lake Como has a water bus system that also can get easily booked out the day of, so I recommend buying tickets online ahead of time.
Milan is similar to Rome - easy to walk if you're up to it and Uber blacks are readily available.
Trains are the best option if you're traveling between cities! I'd recommend booking with Rail Europe as it can suggest paths for you. Stay alert when traveling from city to city. There are professionals waiting to steal from tourists!
Go check out my guide for the best free things to do as well as itineraries and travel tips to make your trip unforgettable.