Lady Hillary here:

As a relatively new performer, be comfortable with your material more than 1/2 hour before you get on stage. Singing in situations where it does not matter what happens (such as in the park) takes the pressure off even if an audience gathers. Singing in supportive situations gives you confidence to get to the next level. Singing by yourself can be the scariest thing of all but it makes you feel even better once you know you have accomplished the part of being able to sing satisfactorily by yourself. [You can be your own worst critic. EB] Once you have done that, you know you can do it again.