Well, I'm out of the (paid) work force myself these days, but I do have a few helpful hints.
First of all, try to have someone role play with you to get some practice. Make eye contact (in most situations) and do not cross your arms. Crossing your legs at the ankles is considered more professional than at the knees. Be prepared to be outgoing. A friend of mine just went for a job interview for an adminstative position and they asked her to sing!!! for them to see if she would.
In terms of questions, take a copy of your resume with you and make sure you KNOW everything on it. Be prepared to state your strengths and weaknesses. When thinking of a weakness, figure out a way to put a positive spin on it. Such as "I have a tendency to take on a lot, but I am learning how to prioritize in such a way that the work gets done on schedule without losing sight of what needs to be done now." (Not a great example, but brain not working right now.)
In terms of clothes, wear something professional. Comfortable shoes (you don't want to be walking funny), pants or a skirt, a dressy shirt, jacket if you want. I think the main thing is that your clothes are clean and not wrinkled and that your outfit is not too revealing. Another thing is that women with short hair tend to be perceived as being more professional, so if you have long hair, wear it up.
(PS -- I took a course on job search strategies and though I find some of these suggestions an affront to feminism, sometimes you have to work the system. Just wanted to make sure no one thought I think that revealing clothing or long hair or whatnot means a woman is more or less capable of doing a job.)
Peace and Good Luck!