Friending locals is important. They have the know how to show you parts of the city that separates typical tourists from the rest of the explorers. You’ll also learn a lot more about the real customs of people in the city by hanging out with them.
City tours often cover the cliche customs, but you’ll learn more about the subtle customs they don’t always mention in the guide books. Like in Vietnam, I learned from friends it is rude to pour yourself beer. Always pour for others and they’ll do the same.
Making friends also means creating a connection to the city and gives you a strong reason to come back one day.