Define your priorities and make a list and then the search begins. In my opinion, recommendations count best and are the most reassuring. For this reason - ask your family and friends if they know a good nanny; you can post fliers at local parenting resource centers, at shops, local schools etc. Check if there is a local nanny training in local area and if there is you can ask for their referral. You can also call private nanny agencies: they screen their candidates, (including criminal record) and it is possible they will represent you the candidate that suits your criteria. The downsize of employing private service is the price: their fee ranges from $1000 to $5000.
Another option is to go online and rent online nanny services: their services are not free, but are less expensive than the local agencies. It is also possible to advertize your position online or in local newspapers, but you must realize there will be a flood of responses and most of them will not be suitable to your criteria. In case you do decide for this option, make sure to define your criteria in the add. Next step would be interviewing candidates that are suitable for the position: ask them anything you need to know it is a nanny for your child you are looking for. Also, besides all the questions and answers you will be given, listen to your gut. If it doesn't feel right, it probably isn't. I would suggest to include your child when you meet the candidate so you can see how the two of them interact.