You may want to take a quick look at my previous post about the nature of delusional thinking. That said, here are some useful strategies to keep in mind when someone you care about struggles with delusional thinking,
First, do NOT jump to conclusions about their beliefs.
Don't judge them for their beliefs.
Just ask questions. Make sure you understand exactly what it is that they believe.
Vincent: They're following me. Monitoring me.
You: Who? Who is following you?
Vincent: The CIA.
You: The CIA? Why are they following you?
Vincent: I don't know. Remember when I went to the dentist? That's when it started. He implanted something in my mouth. In my tooth. He said I needed a filling. Look - see. See - it's back there.
You (looking): Hmm... I don't see anything unusual looking. How do you know the dentist didn't just put a regular filling in your mouth? What do you think he implanted?
Vincent: It's a remote controlled tracking device. Believe me - it's not normal. I can feel it. My primary care doc said it looked normal too. But it's not. They're using it so they can monitor me.
You (summing up the delusion): So, the dentist implanted a radio-controlled monitoring device in your tooth so that the CIA could monitor your whereabouts? But you're not sure why the CIA would do such a thing?
Vincent: Yeah. The dentist is obviously in on it. He must be one of them. The CIA. I don't know why they're after me... But, they are. I've seen them drive past my house 7 times this morning already.
Second, make sure you also understand the emotional consequences of those beliefs. Remember, even if you don't share their beliefs, those beliefs are 100% true and real to the person who suffers from the delusions. Put yourself in their shoes. Imagine that the beliefs are, in fact, true. What would you do? How would you feel?
Back to our Example:
You: That sounds frightening - the CIA following you. Monitoring you. Knowing your every move.
Vincent: It is. That's why I don't want to leave the house. I'm scared of what they will do... I think maybe they are going to try to kill me.
You: Yeah,... Especially since you don't know what they're after... That is scary... Are you also angry? Like angry at them for doing this to you?