OK. I don't want to come over all tecnical, but first of all, conversation clases are not just about sitting down and chatting, whether it be about the weather or a relevant newspaper article.
Your students want to learn something. So, by all means, think of a topic, but think it through and decide what vocabulary one would need to discuss this topic. And then expressions for agreeing and disagreeing. Listen to yourself for a few days, and you'll see what I mean. In fact I'll send you my own list. It's more than "I agree" or " I disagree". Shoot them if they say I AM agree.
But it's things like:
Of course, but don't you think ....
Well, I wouldn't go that far...
Up to a point maybe...
Blah Blah Blah
Then choose a topic, brainstorm yourself all the vocab you need to constructively discuss it.
For example if you're going to discuss LOVE this Valentine's Day, make up a list of vocab from your own experience. Listen to yopurself talk about the thing over the next few days. Watch Sex And The City - well maybe not - and make up a handy hand out with phrases like:
I'm really into guys who...
I can't stand girls who..
What really turns me on is...
Fling
One night stand
Unrequited love
I fancy...
And so on.
Give your students a list of provocative statements or proverbs about the subject, put them in pairs and then have them report back to the general group and discuss..
For example:
Love is blind
All men are pigs
Does love at first sight exist?
Would you forgive infidelity?
Men are from Mars... (or Ohio, see MadridMan) and women are from Madrid.
Anyway. Structure every class around one topic, give them the phrases, vocab, and run it like a talk show.
Just remember that your students are paying and they want to leave the class having spoken and having learned a few new turns of phrase, and who knows , equppied to pick up a new boy or girlfriend. Which will make you redundant.
PS Agood book for theme related vocab is
Longman Language Activator
ISBN0 582 04093.0 (paperback)