好久不见 is famous enough to have entered English as "long time no see", and it really is the opening line. What follows it is the part worth rehearsing, because the second thing you say sets the tone: 你变了 can be a compliment or a worry depending on your face, while 你一点也没变 is safely warm. 我们有多久没见了 buys you time and invites the other person to do the arithmetic.