Always have an application form that requests details of last 3 years residences, contains date of birth, national Insurance number and next of kin details.
Require a copy of a driving licence, passport or other proof of identity.
Always use a tenant credit referencing service such as the RLA's.
Ask for sight of the last 3 or 6 months bank statements.
Beware of people in a rush, or "living with their parents". Often they become a problem.
Try to make an unexpected visit to where they live now - that way you can see how they look after that property and confirm they actually live there.
Advise them to take out Insurance to cover their belongings.
Serve a S21(1)B notice at the start of the tenancy. That is the day they move in. They will usually sign a copy of the notice at that time thereby providing all the evidence you need to prove the notice has been served. This should be done AFTER the deposit has been lodged in one of the authorised deposit schemes.
Think about taking 6 weeks deposit to avoid the scenario where they do not pay the last month rent, and there is still damage when they leave.
Make sure you have building insurance in place which covers "Injury to people residing in or visiting the premises" in addition to your building and your belongings