I think that . . .
I don’t think that . . .
In my opinion . . .
Why do you think that?
Could you give (me) an example?
Can you illustrate that?
What evidence do you have?
Could you explain it in more detail?
Could you provide some details?
Supporting your opinions
Let me illustrate,
For example,
For instance,
To give you an example,
Let me give you an example,
To elaborate,
First, (second), etc.
(These phrases can be followed by details, examples, elaboration, or a summary of your main points.)