When the server asks, "Are you ready to order?" and you are ready, you would say....
"Yes, I would like..."
When the server asks, "Are you ready to order?" and you are NOT ready, you would say...
"No, sorry. I'm not ready to order yet...Can you...?"
What do you say if the waiter brings you the wrong food?
Be nice! "I'm sorry - this is not what I ordered..."