What are the most important qualities to demonstrate in job interviews?

You should prove that you understand what the company does and that you are familiar with it. Also, be positive and radiate a good vibe. The ability to learn quickly, be willing to learn, and be flexible are also important for each company. 

You must have future goals, whether on a personal level or for the company in which you will work, and you must have confidence in yourself and answer questions honestly and kindly.