I had the same issue you are having. I would freak out if the controller said something unexpected.
In the simplest terms it really is just monkey say monkey say back. I know that may sound dumb, but what I do, I don't even think about what the controller is saying at first. I just concentrate on saying back exactly what he told me. After you read it back you can figure out what the controller meant for you to do.
Another thing I did when I was a student pilot is make a template for talking to atc. It was basically a fill in the blank with the required position reports and lingo in there. All I did was write in my tail number and position and everything was written out for me.