I would try for something balanced.

Introduce a grammar point, I would recommend the 2nd conditional (impossible situations - if + past participle + would) as you can have a lot of fun with that and if falls in to the A3 range of the CEFR.

Introduce how to make the conditional (condition clause + result clause) and demonstrate how and why we use them. Use the board to show the clauses can be either way around.

Pre-prepare some condition clauses, put your 'students' in to pairs, have one pull a random condition clause that their partner must give the result clause, for example

S1: If I won the lottery...
S2: I would buy a big house.

Then have them swap. The explaining of the grammar point should be around 7-9 minutes. A minute to explain the speaking task, then five minutes of pair work, in which time you monitor and give input to each pair. If they finish the task early, switch the pairs around and repeat.

This way you show you are able to demonstrate and teach a grammar point and give your students an opportunity to use/practice it.

I would steer well clear of conversation classes in demos or in general. A good lesson should be balanced and introduce new grammar and/or vocab, plus a chance to use it in speaking, writing and listening tasks. Pure conversational classes are not really what I call teaching, more a language exchange.

Hope this helps