However, I know that conversation does not come easy for everyone.
Awhile back, I was reading this post and I loved the advice she gives! A great conversation starter for someone you don't know well is "What keeps you busy during the day?"
Asking this is a great way to invite the other person to open up about their life, but you avoid a potentially awkward conversation by asking about something that could be a sensitive subject (job loss, relational difficulty, etc).
Aside from that question, you could also think of a few other open-ended questions before your guests arrive to ask in case there's a lull in conversation!