Throughout your day you're probably involved with many, many conversations most of which are just not of interest to you.
To be polite though, everyone has their own way of simulating interest.
Here are a few common ones currently in rotation:
oh that's cool
how was it
good for you
i'm sorry to hear that
If you use these words, I think it's best to work in as many of these as possible because repetition is a dead giveaway.
The above is assuming that you desire to keep the conversation going.
If you want to end the conversation, here are few useful phrases:
Act very huffy and say 'I think I've heard enough.' - This is only good when they're telling a lighthearted story. They'll think you're being funny. Suckers!
I have a secret society meeting to attend too. (Having said it's secret society, you won't have to answer any further questions about it by definition).
I must see the Overlord.
I must use the bathroom.
Your story is wonderful but i'm not a fan of the protagonist at all and the plot is full of holes.
Feel free to contribute your suggestions.