It is particularly important to review the answers, and feed them back to confirm that you have the right understanding. There will be some hard questions asked by the people you are interviewing, so you need to be prepared to answer them. Most people are threatened by change, they find it painful, so be aware of this. Try and lead them gently. Use the information you have gathered to build your model.
Graphical tools are very useful for displaying and undersatnading the model.
There is no simple answer. Each situation needs to be carefully and individually considered. Q. People do get offended when you ask them about the processes which they are involved in, especially when they have found an effective method for doing repetitive tasks. How can we lead them through the process carefully. A. Make sure that you do not give the impression of knowing the answer.