Agree with the above :
Good references - I also always check by phoning previous empoyers asking would you employ this nanny again or would you have any reservations?
Punctuality and good health/sickness record
Personal Appearance - looks fairly neat but not overdressed
Commitment for at least a year
Energy - someone who likes to go to the park,run around the garden with the children
Calm - someone who could both deal with a medical emergency and toddler tantrum in a capable way
Seems to genuinely love children and has the 'cuddle factor' and takes an interest in them if they are present at the interview
Can cook not just reheat things and understands good basic nutrition.Can teach basic table manners and will sit and eat with the children.
Good hygiene - I'd check if this is in line with how I like things done
Still with lots of initiative/enthusiasm for the job who can suggest/lead activities/play at the level the children are at.
It is often the case of the nanny and family being the right fit for each other.A good nanny can mould herself to her employer's needs.