Companies Mission & Values/Ethos
This will help you understand why the company does it work and how it goes about it! Not knowing this will go against you in an interview.
The Clients, Products & Services
Make sure you know what the company offers, what it sells or offers to its's clients and the type of clients that use the company. This is a must know!
Have a good understanding of how the company is run and who are the key people for running of the company.
Recent Achievements & News
Make sure you're up to date with all the relevant news about the specific company especially for interviews.
Knowing if a company has potential new projects and the impact/opportunities that they can help in your interview.
Knowing the companies reputation can help you decide if you wish to work that company.
How Long Company Been In Business For
Part of the interview research preparations, knowing if the company is a new business or an established one. Sometimes individuals can be nervous for working for new businesses.
Knowing the type of employees that are in the company can help you know if that it a company you wish to work for and could potentially fit in with the other employees.
If you know who in the company who will be interviewing you, research who they are to help you get an understanding of them before the interview.