^^^
Most people love talking about themselves or their interests so even though you may not be enjoying the conversation, there's a decent chance they are.
Asking for clarification such as saying, "so you feel like . . ." or "you mean you . . ." show that you are interested in what they are saying and trying to understand. Most people like that and then consider you a good person to talk to... or talk at. Even if you know nothing about a subject, it can be easy to show interest with questions. Be honest about your lack of knowledge on a topic and act interested in learning more about it (even if you really couldn't care less). So "To be honest, I never really had an opportunity to get into Dr. Who. What about the show makes you like it so much."
Then the person goes along and talks about it with your occasional input question to keep the conversation progressing. Even if you never end up watching the show, you can use what you hear in that conversation for future ones. Talking to another person who likes Dr. Who and maybe mention, "Oh yeah, I heard about the one episode where . . . it sounded pretty interesting, I might start getting into the show myself."
The perfect situation of course is actually finding someone who has things in common that you both enjoy talking about. I'll admit it's easier said than done. I only have about two people who I can really communicate with and enjoy it fully.