I think it depends on the role, and the show.
I've done everything from "stay in character" (if the role is really demanding), to rest, to goof off.
The funny thing is if a show is particularly "heavy" (as far as dramatically), I tend to want to goof off more... respecting the other actors around me, of course. I only want to "play" if they do too. For some reason going the opposite direction from the tone of the show actually worked to help my focus, mood and energy on stage. I needed those breaks to "lighten up" a bit. It depends on how far you dive mentally into an unstable character's head, too. I tend to "go for it," so there has to be a bit of a time-out period, if possible.
But I think I can relate to Dollypop's answer the best, as an overall response. I like to go to a "quiet place," where I can:
1) Save my energy
2) Concentrate on staying in a given mood (whatever that may be for the show)
3) Warm up a bit vocally, if need be.
4) Focus, focus, focus
EDIT: By the way, I'm not one that thinks "staying in character" off stage necessarily helps. It's whatever works for YOU. And I've known and worked with brilliant actors who break character the moment they're out of the sight lines. It's what you do ON stage that counts.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22
Updated On: 8/11/06 at 02:01 PM