I occasionally have to interview people for work and I'm always amazed how unprepared people are when they arrived. Practice interviewing. Just grab anybody and have them interview for a job. Do it all the time. The practice will take over and you'll come off sounding calm and confident even if you are taco bell BO nervous.
Emphasis on, why do you want the job and why should we give it to you. If they say, "I need a job," I generally don't hire them.
