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 RLAs.
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 Home visit - that way you may see how they look after a property and confirm they actually live there.
Advise them to take out Insurance to cover their and your belongings.
Serve a S21 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, providing the evidence you need to prove the notice has been served. This should be done AFTER the deposit has been lodged in a scheme.
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 Insurance in place that covers "Injury to people residing in or visiting the premises".