"The artist's job is to be a witness to his time in history."
"I wouldn't use the same color in a picture in more than one place."
"My art is about paying attention -- about the extremely dangerous possibility that you might be art."
~Robert Rauschenberg
Combine elements (some pre-existing, some not) into a theatrical collage.
Anytime.
In terms of playwriting we already have an example of a theatrical collage work in Charles Mee's bobrauschenbergamerica. The play is quite literally a collage drawing on the artworks and processes of artist Robert Rauschenberg. The National Gallery of Australia remarks that:
"Rauschenberg's work contains layered image sequences, or image sentences, where the viewer interprets the progression of images as though reading a language system. Rauschenberg's syntax, however, is arranged in multiple, simultaneous combinations and directions. It demands a different kind of looking -- a repetitive change of focus, back and forth, in an analysis of the detail of each individual component image in order to perceive the composition as a whole. While this fragmentation of the composition is akin to the multiple viewpoints of Cubism, it has been more eloquently compared by John Cage to watching many television sets working simultaneously all tuned in differently.'"
Collage employs many diverse mediums (found objects, canvas, paint, etc.) to create sculptural "paintings" on account of the three dimensional objects used in the medium, as well as the heavily layered sections elevated from the canvas. The important thing, for the writer, is that the concern is very much not with a linear narrative (if any narrative at all).
As usual, there are many ways to port this concept to playwriting. I've suggested one below.
Disassociate those individual elements from your narrative (read: try to forget the story you're telling) and quickly brainstorm each individually:
I use an application called FreeMind, but there are many others. This can be done with paper/pencil as well.
Take all of the items from your brainstorm/mindmap and utilize them in your play.
If you're thinking "That's A LOT of stuff," then you're doing it right.
Focus less on the story and more on the theme, the idea, the feeling behind the the story.
With any luck you've plastered your play with a smattering of "found"/discovered objects collaged from your own associations. Perhaps there are additional things you could add? Perhaps you liked one branch of your mindmap better than others? Perhaps you wished you could have also done visual, auditory, and video research. If so, feel free. Perhaps you just ended up with a mess of a something made out of words and you hate it. If so, throw it away. Try something else: new or familiar.