The way I prepare a scene has been morphing of late. In Michael Mendelson's scene study class, I began doing character histories--or rather, autobiographical reports from key moments of a character's history as it pertains in some way to the action on stage--and have found them productive. I do not find that the 'facts' I invent--the detailed fictions--are important in themselves, but rather they're ways for me to activate my objectives and obstacles--my action--on stage. Yes, I plumb 'as if' scenarios from my own life and memory--those of David Millstone--but I often find that the very nonfictional character of my own memories and personal aspirations or fears can become as much a block to authentic embodiment of a character-in-a-scene (I never think about trying to embody--or build--a "character," only a "character-in-scene," which is to say, an "action") as a spur. My true experiences do activate me, but I also find myself quashing what they reveal... to myself. Writing fictional character histories--though, of course, pulling extensively from my own experiences and exploiting my own ghosts--gives me the slight distance I need in which my imagination and empathy can flourish.
I don't believe I'm alone in this. As I understood his book, Meisner did not advocate trying to prepare from personal experience alone, but advocated for imagination and outright fantasy; I'm finding that using them brings me deeper into the experience of the character/action, as long as I don't attempt to intellectualize or hold on to the details of the backstory I've dreamed up.
For me, character/action prep is about dissolving my own resistances and activating empathy. From pages and pages of backstory, I find that it is some essential sense experience that stays with me, and carries the emotional resonance of all the details I can then let go. For instance, from my preparation for Mr. George--in Valentine's Day, by Horton Foote--what stayed with me was the invented 'memory' of the look on Mr. George's mother's face when she saw him playing with black children on the plantation Mr. George would later inherit. That look was all I needed to activate everything he was about, long after I 'let go' of the history I'd written in which that look was embedded.