Having just gone through it I think you basically need a) list of stuff to ask them when they get in touch and what you're going to tell them about you / area / what you offer etc b) list of telephone questions c) contract.
Contracts are apparently a legal requirement. I was suprised to discover your a/p is less a kind of family member (as they all think) and are legally an employee with holiday rights etc. You legally have to have a grievance procedure etc.
Our contract includes room, money, travel here, notice period, what's dismissable behaviour, details about phone use, internet, weekends, inclusion in activities, review, curfew, alcohol, medical and dental treatment, friends visiting, cleaning own accommodation etc.
I also have a document which has the a/p routine and schedule.
I would also say that it is a very big and hard decision to have someone you have never met come and live with you for a sizeable period of time. It's pretty amazing it works at all and prudence probably pays off.
I am (after a terrible experience) very careful in recruiting and twice recently have lost good candidates with whom we we had chatted a lot and were getting references to other families at the last minute who I suspect were less demanding in the recruitment process.
I now also think experience and probably age count for quite a lot.