I seem to be finding many topics far too late to be of any real help.

First of all, relax. You'll do yourself more harm than good before an audition by fidgeting or becoming nervous.

Second, when you act, act. It all depends on the play, of course, but you need to do some in-depth analysis of your character. If you are playing the 'villain', does that character really believe he or she is the villian? Most likely not. They will likely believe that they are right in what they are doing, whatever that may be. Why would they act this way? What motivates them? That's the dividing line between drama and melodrama, or, as I like to call it, "this is my character" versus "White hat=good guy, black-hat=bad guy"

Read some texts on the subject. Either simplified guides to Stanislavsky's Method or other books on acting which will also incorporate it. (The reason I suggest first reading simplified guides to Stanislavsky is that if you don't, Stanislavsky's actual books are really difficult to follow. They were pieced together from his notes by his students after his death.) I actually have, in my collection "The Complete Idiot's Guide to Acting".

Anyway, I hope you got your part. Break a leg!