First thing to remember is, the audience want you to be good, so they are on YOUR side.
Secondly: BREATHE - breath is food for the voice.
Don't talk too much - I've heard performers, especially older ones talk more than they sing. They came to hear songs, not speeches.
If you play a guitar, don't "thrash" it, they'll hear it well enough, it's you voice they came to hear.
Keep you head up and sing OUT - I've seen so many beginners with their heads down, singing to the back of their guitar. Just makes your voice muffled.
Make up a programme so you know what you are doing in advance.
A 45 minute spot requires around ten songs,