One of the basics you need to create a user-friendly interface is that you should know the user. You should know what are his goals, tasks, abilities, workflows, the environment, etc.
So one of the first step in the user-centered design process is to collect the information. One possibility to do so is to interview endusers as well as stakeholders.
A the beginning the usability expert should collect the questions he wants to ask and should always have in mind the general purpose of the interview. The perfect place to interview the enduser is the environment in which the application will be used, so for example in his/her workplace. The usability expert shouldn't ask question after question but rather let the user talk about their experiences and the expert should observe the behaviour of the user.
Several websites provide lists of questions that can be asked during an enduser or stakeholder interview. One website that provides a lot of information about each step in the usability process is usability.gov. They also provide a list of questions (.doc) that can be asked to the team at the kick-off.
Another good resource is the list of questions by Jared Spool and also the article "Putting context into context".
If you have any other interesting sources/links you're welcome to leave a comment.