How to efficiently design Firebase database for Home service Booking application?
your database should look something like this object: 

{
  users : { uid, ... },
  bookings: { id, uid, ... },
}


And you access each user's bookings by querying with a condition that the column uid matches the user's id, by using firebase.auth().currentUser if you're using firebase. btw you should Cloud Firestore for better scalability and faster queries.