"I've done it before so I can do it again."
"I've done harder things than this. I can handle this, too."
"I've done something similar. I'm sure I can do this."
"If he can do it, I can, too."
"I've prepared really well. I'm ready to do this."
"I was born to do this."
"I've visualized myself in this situation and know what I need to do."