If they haven't aske, make sure you tell them WHY you are interested in the job at the end of the interview.
When given the opportunity,ask job-related quesions that ar not about salary or benefits.
If you are offered the job on the spot-accept it there and then. You can always turn it down later if you are successful at another interview.
Thank them for the interview, remember even if you don,t get the job-a positive last impression will stay in their mind and they may contact you in the future for another position