[Kate*]

Aside from writing down what you want to say, which I have also done and it really helps, I would suggest starting with places where you don't really want to work, but would be okay with. That way you get practice while the pressure's off and if the call, application, or interview goes bad you didn't really want to work there anyway. There is a risk that they might hire you and then you're stuck in a job you don't really want, but you could always consider that practice too.