What's a good first-time Italy itinerary?

Rome, a Tuscan base, and one northern city — flying into Rome and out of Milan or Venice so you never backtrack. Something like four nights in Rome, four or five in the Tuscan countryside with a car for that stretch only, then three or four in Venice or the lakes. It gives you the ancient world, the Renaissance, the landscape people picture when they say "Italy", and food that changes completely every two hours on the train. Open-jaw flights cost about the same as a round trip and save you an entire day of retracing. Book those first; the rest bends around them.