I've been hosting on airbnb five years. Here are my two tips:
1) I always respond to guest inquiries promtly and engage them in a conversation about their trip and needs and such (through the airbnb message thread). More importantly, I pre-approve almost every inquiry within 24 hours. It does not preclude another guest from booking and it expires 24 hours after you make the pre-approval. If the guest is not ready to commit that's fine, they can ignore your pre-approval. You can send another pre-approval when they are ready or send them a special offer. On very rare occasion I will decline for cause.
2) I mainly reply to guests through the airbnb message system ONLINE. Even though all the emails say "Respond to (guest x) by replying directly to this email", I have read many reports where hosts replied by answering the email and the message did not go through. It has happened to me. Then we get dinged for poor response rate. If you want to reply to a new guest inquiry quickly, while you only have access to your smartphone or pad, go ahead BUT when you get back to your compiter (and always within 24 hours) check the message thread and make sure the response shows as sent. If your dashboard still shows that warning "You have 11 hours left to respond to guest X" then respond again.