DON'T think, DO :) don't think too much on thinking about little things of big things. It'll lead you to stress and maybe anxiety. Instead of thinking about being on stage in front of people, just do what you were up there to do. Perform, sing, dance, etc..
Dont look at the audience pay attention to what you have to do or the person your gonna work with take deep breaths from your nose if you get nervous and exhale always think possitive things and dont forget to smile