I have been getting back to my audition coaching lately, and speaking with singers, I am reminded again that one of the important things you have to do is actively "create" the world in which each of your arias resides.
This of course is easier if it is a role you have done, but even if you haven't done that, work on mentally creating the context for the aria, and then staging it as part of your preparation - this can prove to be as important as diction, pronunciation, technique, etc. As a matter of fact by having your physical presence in your audition take center stage (sorry for the pun!), you won't be thinking of your voice all of the time, which, at least for me, was one of the pitfalls of most of my auditions.
As I have said before, even though you will stage the aria, that doesn't mean you have to use all of that staging in the audition - but the "residue" from that staging work is going to make you more physically aware and comfortable in the audition itself.