After starting to look for a nice family to go with, I recommend you to think about the next list of tips:
Country: It's a basic. In my case, I was sure that I wanted to improve my English so I focused on English speaking countries. Besides, I had been in Ireland before and I was aldready in love with the country so it was my first option. And don't forget that choosing the country, you'll be choosing what new culture and routine you may have in the future.
Children age: You must decide if you are up to mind babies, teenagers... Personally, I preferred not to take care of babies and I took care of Emma (6) and Jack (10).
Village/town/city: This is a really important thing to think about. I faced a challenge during my experience because Mountmellick was too small and quiet and there weren't more au-pairs living there. A small town might be nice for a short-term experience but I would recommed you to choose a bigger place for long-term experiences.
Au-pairs in the area: As I already mentioned on the previous tip, it will be very important to have other au-pairs living close to you. You will need to meet them after difficult days and they will support you and understand you because they might have had similar situations. Besides, everybody needs friends!
Animals: If you are an animal lover as I am, it might not be really important. Anyway, you must always ask if the family has any pet. In my case, Lennon was really helpful and I really miss him since I came back.
Money: This is a really important thing to clarify and talk about before starting your experience. I recommed you to sign like a contract - even if it's informal - between both parts. I lived some uncomfortable situations related to money - not getting paid for some days worked or being forced to ask to get paid - and I felt really sad/dissapointed/angry when it happenned.
Your tasks: Here I'll talk again about the importance of signing a contract. Someday you might be asked for a variation on your tasks and it's up to you to decide if you agree or not because you'll already have signed a contract where your obligations are specified.
Your room is your room: Basic question. The ideal would be to have your own room and bathroom but it depends on the house where the family lives. In my case, I had Emma's room and I had to share the toilet with the kids and the shower with the whole family. It was ok for two months but I wouldn't like that for a long term experience.
Holidays: If you choose to be an Au-pair for a long time, you will have the right of taking holidays. I recommend you to clarify this topic with the family before you start.
Flights: Who will pay for them? That's another point that should be on the contract. Some families agree to pay the flights and some of them don't.
Skype interview: messages and emails are not good enough. I strongly recommend you to have some Skype calls because you'll get a more precise idea of the family and how they are.
And then... YOU'RE READY!! But remember: not every day will be easy peasy: you'll face difficult days particularly during your first weeks. However, life is like that 24-7, life doesn't care if you are in your hometown or not. So be possitive and face the challenges: you'll suceed!