Express Your Enthusiasm And Desire For The Position
All things being equal, people hire candidates who want to work for them. You should close with, "I'm very impressed with what I've learned today. There is no doubt in my mind I can do this job and would do it well. What would be the next step?" or "How do my qualifications compare to others you are considering for this position? Is there an area where I fall short of your requirements?" (If so, address the issue!) Let the interviewer know that if hired, you'd be prepared to give two weeks' notice today!
Last, always send a follow-up thank you note to the interviewer.
That's it! Good Luck, and remember to smile, relax, and have fun with your interview. . . and call me when it's over.