I know I've already answered, but I suspect there's some confusion about the next step...
When you ask about creating the best possible collaboration, I suspect it's a hierarchy. At the bottom of the hierarchy are the basic needs for the collaboration, like terms of work and expectations that ensure communication and meet the needs of all parties.
If we take it a level up, we're approaching artistic collaboration...the sharing of ideas, improving/fleshing out/adding to/revolutionizing what the writer's brought forward. An example of this is your collaboration on the DWPFF story, and how through a character sketch, your artist helped turn a short story into something much bigger and drawing on more influences.
SO...the next step seems to be facilitating collaboration.
We've gotten past the awkward first dance, the shuckin' and the jivin', don't put your hands THERE, mister!, and now it's slow dance time and...it takes two to tango (even though a tango isn't a slow dance, and I've totally stepped on my partner's foot, and...oh, forget it!).