I have been told when the interviewer asks, "if you have any questions" it is always best to say something. The reason is it shows your interest in the company. Showing an interest means you are serioius about getting the job. You may want to ask if there is an opportunity to progress in the company. This demonstrated your committment to stay with them for a long time. Another good question is if the company has a pension plan. This again shows you're intersted in staying with the company for the long run. You may even have a question during the interview. Just try rememering it and address it when the opportunity arises.
This is what I have always been told as well. I generally ask what I want to know that they have not answered in the interview questions already. Example: I will ask about what they are looking for in a person to fill this position, or is there room for advancement or something like that.