A lot of us make the mistake of going and auditioning without really having any experience singing to an audience, let alone in front of critical judges. It's important to know your strengths and weaknesses.
Singing is a lot about your voice, everything else comes after that. Remember to take HONEST opinions from TRUE friends about your skills, preferably from people who are already part of the music industry or the music fraternity in your city.
Interact with people who have bands, in fact if you love singing so much, create your own band. There is no better way to improve than to sing regularly. You should try and get into the gig circuit to gain experience, not just vocal but also performance. Learn to appreciate different styles of music, listen to jazz, rock, Brazilian, Hip-hop, RnB. Listen to singers who've shaped vocalists today. It's always a good thing to be versatile, though creating your own style is even more important.
A few pointers below could possibly help you better your chances at your next audition.
Sound Professional
Get a control of your vibrato, different textures, dynamics and individuality. Remember to sing songs within your range. Transpose if need be, no one wants to hear you screech. Show off your vocal prowess, but don't do something that sounds bad. Remember a cappella music needs to sound pleasant. Remember sounding powerful doesn't mean shouting/ shrieking. Look Professional
Dress up like yourself and not like a court jester. Your clothes maketh the singer in you. Don't put your ear to your finger when you're auditioning, its pointless, because your not singing on stage where you can't hear yourself through all the band noise. Your singing acappella. Duh! Stay Modest and Grounded
The last thing anyone is looking for a self proclaimed DIVA. Remember you still are a "nobody" one unless you've been gigging and singing for many years. Don't throw a tantrum especially when you don't deserve to.