A quick perusal of online resources yields things from the most basic at the Vocalist site ("Walk gracefully or stride across the room/stage with purpose, keep your head up and look where you are going."), to the more involved discussions that take place on sites such as the New Forum for Classical Singers, to Kim Pensinger Witman's astute blog of the Wolf Trap Opera 2006 auditions as told from the auditioner's point of view.
In fact, aside from entries in Ms. Witman's blog, there does not seem to have been much information from the pianist's point of view on the audition process. Here are some excerpts she posted yesterday:
On what makes a first-rate audition pianist:
"Listening. The ability to put the playing in subconscious mode and use most of the conscious mind to take in all of the details of the performance and become a split-second collaborator for singers the pianist has never met."
On what an audition pianist needs:
"Pianist-friendly materials. Books that stay open. Sheets of paper that are held securely in place by a binder. Double-sided, please. And not in shiny sheet-protectors.
Clearly-marked cuts. You don’t want your support system to have to guess where the next measure is.
Easy-to-find arias. We ask for aria #2, you smile and acquiesce, and begin to compose yourself to assume the new character. Meanwhile, the pianist is fumbling through your notebook or anthology.
Clear intentions. Know what you want to do and indicate it. By preparing for phrases with a breath that indicates the downbeat. By choosing a tempo and sticking to it. Indicating the tempo of an aria by conducting it, snapping it, or singing a phrase before starting never works. Never. I know you don’t believe me, but it doesn’t. Sing with clear intentions and a good pianist will be with you."