During the interview
Parents: During the interview process make sure you are clear on what your needs are and what the responsibilities of the nanny/sitter entail. If your nanny will be asked to wash windows, walk the dog, or tutor the kids in algebra, tell her now!
Nannies: Be honest with your employer and with yourself about what you are willing to do at the job. If some of the responsibilities include playing outside with the kids and swimming at the town pool but you hate to get wet and would rather knit than kick a soccer ball, maybe this job isn't for you. Simply, don't pretend to be a lifeguard if you can't swim. It won't turn out well.
On the Job
Parents: Keep talking -- All good relationships are based on communication. Check in with your nanny weekly to make sure everything is going smoothly. Even if you're the passive aggressive type, talk about any issues or concerns and don't let them fester. Better to deal with problems immediately, than let them stew.
Nannies: Don't be shy. Speak openly with the parents about what is happening at home and with the children. Your job satisfaction is important to everyone. Parents do not usually want to replace their nannies and sitters -- it's emotionally exhausting and time consuming. So they want you to be happy. If you have any problems, speak up so any issues can hopefully be resolved.
Parents: Unless you've hired a psychic, chances are your nanny is not clairvoyant. You should be direct and specific about your priorities and things that you want done. If you want your kids to be fed broccoli and spinach three times a week, put it in a dinner schedule. If you want to schedule play dates with certain children, make it known and be specific about who the children are and when the play dates should occur. If homework needs to be done before dinner, make it clear that this is a priority.
Nannies: Some parents are more intent on creating schedules and knowing what has happened each day. Other parents take a more relaxed approach to overseeing their nannies and sitters. But parents are interested in the day's events. Communicate with the parents and if you are asked to feed the child a certain food or read for 15 minutes or have the child practice the piano, let the parents know that these things have happened. Be pro-active in the communication.
Parents: Just because you have a chicken defrosting in the fridge and some fresh corn on the cob on the counter, don't assume that your nanny will be cooking it that night for your kids unless you tell her. And don't assume that because you gave your nanny a day off or paid her a full salary for working fewer hours that she will make this up to you and stay late or work overtime without pay. You must communicate what you want and what you expect. You may not always agree, but at least you're not guessing.
Nannies: You want to be able to plan your life and your schedule, so make sure you ask things like which holidays you can take and when you can expect a raise. If you assume you have Columbus Day off only to find out that you're expected to work, resentment can develop. If you assume you'll be getting a raise at Christmas and you don't, again, you may be bitter. Parents can forget to tell you these things - remember it's better to ask, than to assume.
Parents: You may want to get emotionally close to your nanny and fold her into your family, but not everyone is comfortable with that type of intimacy. Respect personal boundaries and possible cultural differences. Your nanny may feel like family or like a close friend but that doesn't necessarily give you the right to probe about her boyfriend/husband/children or even financial situation. Respect privacy and don't volunteer your opinions about her personal life.
Nannies: While some parents may want you to have dinner, watch a movie or go on vacation with them, others don't. And while parents may freely discuss personal matters with you, remember that you are in a professional relationship. Yes, you should feel comfortable to have an open communication with the parents, but best to keep judgment about their parenting style or lack thereof to yourself. Parents want to feel that their rules and choices in how they raise their children are respected.