Apologies, another parent here. I wanted to add a few things that come from personal experience and the experience of close friends:
Be clear about the duties and responsibilities you'd like your nanny to undertake.
Discuss how/when you would like holidays to be taken. With advice from the agency, we agreed with our nanny that she would take half of her annual leave at times that she chose. As we travelled for a month over Christmas every year, the other weeks were taken at our discretion.
Think about bereavement leave - like sick leave, make note of the statutory number of days. Hopefully, it won't come up but if it does, you can always decide at the time if you'd like to give her more than what's been agreed.
The nanny should always have a charged and fully functioning mobile phone with her. The phone must have a current contract or have credit on it so that she can make calls and/or send text messages especially if you are trying to reach her. If voice mail is important to you then you should also detail that.
If you ever need to make any changes to the nanny's duties, responsibilities or hours, write up a new contract and go through it with her. You should also draw up a new contract whenever you increase her salary/hourly rate.
Be clear about whether you're happy for your nanny to smoke at all. II wasn't, so there was to be no smoking at all even when outside and not even outside when our child was asleep. I mention this only because a friend let her nanny smoke in front of the children when they were outside. It then became a problem and she didn't know how to address it. For me, there was to be no smoking because we're not smokers and we also wanted to ensure a good example was being set in front of our child.
If you have hired//are hiring your nanny through an agency they should be able to give you contract templates. If not, then here are a couple that may be of assistance:
MODEL CONTRACTS FOR NANNIES TO BE - Nanny World
https://www.google.com.au/url?sa=t&rct= ... 8758,d.dGc
http://www.payefornannies.co.uk/parents ... tracts.htm
Good luck with it all. It can be a minefield but if she's a good nanny, it will be an excellent experience. Our child still adores her nanny, even though it's been years that she left us (as our child was too old for a nanny not for any other reason.)