During this video you can see how one of Sia’s main techniques for songwriting is to create a freestyle vocal melodie over the producer playing the piano part chosen, this is how she begins her process, before even thinking of a topic, she starts from a different point.
I have two things to take from this, one being that, some songwriters will, instead of relying on coming up with some inspiration to a beat in a very laidback way, like The Weeknd and Daft Punk, or being very strict incredibly certain about how the beat and track will be before writing lyrics or vocal melodies, like Eminem and Rick Rubin, Sia and her producer take a route pretty much in between the two other examples, by using a certain method to come up with ideas and inspiration, in a laid back way. The second thing, is that during this, Sia’s producer isn’t even really producing in the standard sense, in fact he is extending the role of producing, to supporting the songwriter and giving them all the help they need to create a song, essentially giving the songwriters the tools they need to work to the best of their abilities, something that all producers should be good at, and all succesful producers excel at doing.