I boost the upper mids just a bit and add the slightest amount of compression, mainly to handle peaks. I'm not sure of the settings, since I do it by ear, but if I had to guess, I'd say it's maybe 2dB at around 8k and no more than 2 or 3 dB of compression at a ratio of 3:1.
An audition, I might process as though I'm the producer, assuming that my audition is going to be presented as is. (I can't imagine a producer getting 100 auditions and producing them all for the client. He's just going to send the VO tracks and say, "pick one", right?) Once I have the gig, however, I like to leave it to the producer. And I like to get to know the producer's work, so I can tweak things on my end accordingly. But if a producer says, "give it to me unprocessed", I oblige.