Engagement with your subject.
What do I mean, well for wildlife, landscape etc, its more about knowing your subject.
For people photography its about talking to your subject, involving them in the picture taking process.
With a professional model you can focus more on your picture taking process, your lighting and technique. Professional models know what its all about, but you should still involve them and keep their interest.
For people who have never attended a photographic session, then engagement is absolutely critical. They should be your primary focus, the technical side of photography really needs to be effortless and not really require any real thought.
Know your subject and engage with your subject. Your picture will improve.