Search the company's web site, GlassDoor.com, and any other sites where there may be information about the company. Take note of the real world things that are happening at the company and ask questions about them. For example, you may find that a company recently rolled out a new product and you can ask something like 'I see that you recently launched XYZ product. Are there any other markets that ABC company is trying to break into'.
If you already know the interviewers, I suggest looking them up on LinkedIn to get a better understanding of their background as well.
Back when I interviewed with my current company, I researched my interviewers ahead of time, and found commonalities with several of them. That way, when I came in to interview, we might talk about our interests, past companies, or other things to help break the ice before we dove into business.
Establishing a frame of reference on the following should be beneficial in your preparation.
you should tap into your network and ask for opinions on the company. “Word on the street” can be a good source of information, but always take these opinions with a “grain of salt.”
When researching a company, I would focus on the company's core values, mission statement, leadership team and products.
What are the services / products that the company offers?
[R]eview recent press releases to learn what is new and exciting in addition to what some of the key challenges are they are currently facing.