Dear viali,
Well I suppose there are a few around from GP to pub etc but if you start on that route you'll be psychologically hooked - i.e. eventually ruined.
That's rule 1.
Rule 2 is to accept that the worse might happen - say to yourself: "O.K. I might faint during the audition, if so, that's fate and I will deal with it when they bring me round" - but deep down you know it will never happen.
Rule 3 is right from the start of the audition day look at your watch and say IT WILL ALL BE OVER IN x-HOURS!. Don't keep looking at your watch but whenever you do or see a clock, knock the time down so now it will all be over in y hours etc.
Rule 4 (sorry, old story) when waiting the final 30, 15 etc min slowly breath deeply and keep on with that mantra: it'll all be over....in z mins.
Finally at night or at almost any time before, face the fact: "Well I can't do anything about it now so I may as well sleep or whatever"
I spent many decades giving public scientific presentations and they were my techniques (nervous every time of course, you never crack that bit viali).
Oh if you can, have a glass of water at hand in case your mouth starts to dry up 'cos of nerves, otherwise have a small fruit gum about you person and speak with it stuck to your teeth - many actors do this.
You'll be great and even greater if you do it through your own guts.
Good luck but I'm sure you won't need it,
SIQ.