The basic facts that you should learn about company include: location of company headquarter and branch offices, when company started and who started the company, how many people working in the company, etc. To learn all these things, you can visit the "About Us" and "Mission Statement" page of the company website.
3. How company is different than it's competitorsLearn about the skills that the company values and looking into a candidate. For this, check out the job post and visit the "Career with us" page of the company website. This will help you to represent yourself as a strong candidate for the post
4. Company Clients, Products, and servicesThere are competitors also for every business. What will you answer if the interviewer asks "what attract you to the company?" Studying about the differences compared to the nearest competitor will help you to answer this.
5. The Company work cultureFind out the type of Clients Company have (if possible) and the products or services company offering. This will give you an idea about the type of Work Company doing, that you need to do after joining. Go through the about us, blog, case studies or other related pages on the company website.
6. The organization structureWhat kind of work Culture Company follows? Is the work culture providing a good working environment for employees? Is the company doing anything for employee's growth extra? All this information will give you an idea if the company is fit for you or not and help you in preparing better for the interview.
7. Recent event or news about companyTry to find out the organization structure of the company. This will let you know about the future scope and growth of your post in the company. This will also give you an idea about whom you report while working on this post and responsibility level.
8. About the person interviewing youRead about the recent news and updates about the company. You can find a "Press Release" or "News and Events" page on the company website. You can find out such information on social media also.
The more you know, the more confidence you get and prepare better for the interview. How much detail you know totally depends on the job you applying and time you have. Like if you are applying for any junior level post, then you don't have to worry much about the information about who are board of directors, who running the company and who are the clients, etc. But if you are applying for any managerial level post then you have more focus on such information.If you know the person, who going to interview you, then try to find out more about the person. Dig out on social media like linked in to know about the experience, work history and interest of that person. This will boost your confidence and help you in connecting with them during the interview.