Make it sound easy, when you sing. Make it sound like it takes no effort and no thought. Make it sound like pure feeling and as if the words were written by you. Don't break character. Have most of your attention on the audience, not on how you sound or how you look or how you move.
If you don't perform like that, the audience feels ignored, neglected, and even cheated. They feel as if they have been lied to. Are you there for them or for yourself? That sounds simple, but if you are not there for the audience, why are you there?
Bare your soul. Drop your inhibitions and tear down your walls. You are just singing to people. You have nothing to hide. Your past doesn't matter. You can't change anything about the past. Future hasn't happened yet. The only thing that matters about the future is what you do in the present. That will directly affect your future. You should have learned from the past. Keep you attention on the audience and on the present moment.
Do you know what the past is for? It is the place to make your mistakes, learn from them, and to get ready for the "now". The past is part of preparation. It is why you are who you are. You are not your mistakes. When would be a good time to let go of the past? Next week? Tomorrow? How about now?
If (while performing) you make a mistake, instantly let go of it and make the rest awesome. Make the next part better or prettier or more intense, if appropriate. Most people remember the awesome parts. The critics, who hang on to the mistakes, should just stay at home and keep out of our way, if and until they learn to be artists. So, if your attention is on what others are thinking, it is actually on yourself and your anxiety about that. Give all you have, as if everyone is NOT a critic. The truth is that very few people are critics. Most people go out to have fun and enjoy, instead of trying to destroy others. The critics can go out and fight the wars while we make our art.
If you think everyone is critical, maybe you are critical. It takes no special talent or hard work to notice what is wrong. It takes very special talent to be great.
When the effort is put forth and added to the talent, the magic begins. Prepare to deliver. Deliver. There is joy in performing, unlike any other joy. Don't let others take that away from you. Others need to find their own. It is not about proving anything. It is not about showing off. It is not about being ignored when you were a little kid, so now you are making up for it. It is not about competition. It is about the best of you, unmitigated, unadulterated, and your bare soul is shining through while people bask in its light.
There will never be an absolutely perfect performance, but there are performances which are absolutely artistic.