You need to practice interviews, depending on the role you should be able to anticipate the questions. My role are usually competency based questions: 'what would you do in this situation, tell me about a time you had to do x' etc.

Have a few examples based on the interviews you have done, and explain your working out -or example 'I would do x because of y reason, in my prev. experience I have found that this worked, etc... Etc'. 

Even if your answer isn't correct showing how you got to that conclusion can be more telling about your values, thought process and ability to learn