One of the things that makes auditions so terrifying/excruciating/difficult is the power dynamic. The people on the other side of the desk or camera are the ones making the decision on who gets the gig and who doesn't. And when we NEED those people to choose us, the energy in the room gets really hard to deal with, not only for the other actors in the room, but for the decision makers too.
How does one get past the neediness? Observe an audition from the other side - be a PA or a reader or find some other way into the room and you'll see how many factors go into casting that you never considered.
More importantly, cultivate an audition attitude. Lighten up and don't take it so seriously. Get to a place where you can take approval seeking out of the equation. Know yourself. Do your homework, take classes, get comfortable with the process of auditioning.
And flip it - the people on the other side of the table need you! If you come in and blow the house down, they can relax - you made their script sound good, their concept works, their story makes sense - because of you and your skill and talent.
And you might just want to listen to the song I've got below. I often make sure that the last thing I do before I leave the house is kick off the audition shoes and dance and sing along w/Jill Scott. And I take the amazing ladies of The A Group to the audition with me in my mind, to back me up with moves and harmony and all their red sequined awesomeness.