How do Italians greet each other?

Buongiorno until roughly mid-afternoon, buonasera after — and use them out loud when entering any shop, bar or small restaurant. Not greeting the room when you walk in is the most common unintentional rudeness Americans commit. Ciao is informal and reserved for people you know; with a stranger or someone older, buongiorno is correct. Handshakes for introductions in any formal context; two cheek kisses, left first, between friends and family only. On leaving, arrivederci. This costs nothing and changes the temperature of every interaction you'll have that day.