If someone suddenly asks you, "Are you busy tomorrow?" regardless of who they are or the situation, whether it's a phone call or a message, you should unhesitatingly reply, "Yes, I have plans tomorrow." Then ask, "What's up?" Do not first reply, "Do you need something?" or say "I'm busy," and do not reverse the order. When others ask if you're free, they are usually looking for your help. By saying you have plans first, you hold the initiative.