Final task: how will the questions change?

I have learned lots about interviews through conducting my own interview in my preliminary task. It has helped me to understand what types of questions I need to ask in my final task. In my preliminary task, I asked very open questions which helps and encourages open discussions. 

However, I believe that the questions I asked in my preliminary task were valid, but don't believe that they directly correlate to my topic. I feel as if the second half of my interview was much more substantial than the first. 

The conversation first started to change off of topic, which I do not want to happen in my final task, therefore I will be making sure that the questions asked in my topic are open but don't invite the conversation to go off-topic.