There's a great series airing on BBC2 at the moment: 'Secrets of the Pop Song'. It's an intelligent and absorbing documentary on the craft of writing pop songs and each week it also pairs Guy Chambers (many hits for Robbie Williams, etc. etc.) with others to write a new song together whilst we watch. Last week he made a ballad with Rufus Wainwright and this week a 'breakthrough single' with Mark Ronson.

Their collaboration process looks the same as when I'm writing with a partner, except their solid industry experience shows through, plus things are greatly helped along by Guy Chambers' multi-instrument abilities and formal music training. So one obvious 'secret' is that he is able to very quickly translate ideas into actual sounds, greatly reducing the trial and error cycle and enabling things to stay fresh whereas an amateur like me ends up spending more time on that cycle.

You can also notice that there is an assistant doing all the DAW software work, so the writers are able to concentrate 100% on the right brain stuff whilst the assistant takes care of all the left brain work, whereas we have to do both - which isn't ideal.

Here's the iPlayer link - I assume it will work outside the UK and there are no copyright blocks on it, etc.
'Secrets fo the Pop Song' - first two episodes

Songs web site
YouTube Channel
BIAB 2019
Cakewalk by BandLab
Studio One 4