Running a pr focus group

We had this question sent to us by Sarah Charles...

Hi Louise,

We are focusing (for the first time) on a PR and marketing plan, and have decided to run a focus group to try to understand the public/clients in our area. 

We have offered free haircuts as a way to entice them in to the salon, and we use them as models for our in-house training 3 times per month, so everyone is winning. 

The problem is that I'm not sure what questions to ask. Are there specific questions I should be asking?

Thanks,

Sarah