You want to get a good feel for what the job entails - don't assume that everything is included in the job description you pulled off the website. You also want to understand how the role fits into the overall company structure and the areas with which you will be working. Also you really want to get a good feel for the company culture. Is this the type of place you can see yourself being happy and successful in?
Candidates that do their research and have questions specifically about the operations/products of the company are more impressive. Hiring managers appreciate candidates who really try to understand the job, how they fit into the company, and where their career path may be.
Here’s a good question to ask: "Can you please describe the culture of the company?" The interviewer should be able to do this and you can get a sense if it is a place that you even want to work. You can also ask, "What do you like about working here? Is there anything you dislike?" These answers can be very insightful.


Lotte van Rijswijk
So don't forget to prepare your questions -- it is ok to have them written out and for you to refer to them. There’s no need to try and come up with questions in the moment. Come prepared!