I usually overcome fears like this by polling as many people as possible to verify that I'm as good as I think I am. It helps me boost my confidence when others boost it for me. Sounds arrogant, now, but it does work.
I encourage you to sing/play in front of your friends and family as much as possible. Then, when you are in front of strangers, try to imagine that you are still in front of friends. Also, when it comes to college auditions, if at all possible, network beforehand and try to meet some of the people who will be judging you. I'm very good friends with a woman who is earning her PhD in choral conducting, and has not only gone through many of these auditions, but now, sat through and judged many more. I'm sure to a stranger she seems intimidating, but anyone who has ever met her in real life would not be scared, she's that down to earth and kind. I imagine most in the industry are actually in your corner, and not against you. They are looking for talent but willing to praise all attempts because they are usually just passionate about music and others who are also.
Consider your judges future peers. Have confidence in yourself. Fake it till you feel it. It really does come with experience and practice.