I haven't had an au pair for a couple of years, but I've had a few over the years, some good some bad.
I would say interview if at all possible, which means seeing au pairs who are already in the country. Lots of au pairs look to change families, sometimes the dynamic doesn't work, sometimes they're treated badly (I've had a couple of escapees from really bad situations - unbelievable how some people behave) or sometimes they come to UK, and realise they want to be in London, but have somehow ended up in a hamlet in Devon. Anyway, there's always plenty around.
http://www.aupair-world.net was always good for me.
When you find an au pair be very clear at the beginning what the house rules are -i.e if they go out that you expect them back by x o'clock if its a weekday, yes or no to them having friends round, a good idea of their rota, and when you want them around. I think the legal hours are 5 a day, unless you pay extra. But be clear when you want those 5 hours, i.e its no good her doing all her hours in the morning to suit her so she can then clear off for the rest of the day (it has happened to me) so if you want her around for bath time etc, make sure you get all that straight. I gave my last girl £60-£70 a week, she did 5 hours a day, which included housework/ironing/dog walks, occasional school pick up and 1 - 2 nights baby sitting. Obviously they need their own room, helps if you can put a tv and maybe stereo in there so they can have their own space. And also you provide their food.
Its a bit of a mine-field, and I wish you luck.When it works, its wonderful, I have 2 lovely friends who were my au pairs (both now married to English guys and settled here!) When it doesn't work it can be bloody horrible, so my last bit of advice would be, and others may disagree, but if you don't feel its working well with a girl, don't wait too long to change things. I'd say a month maximum is enough to know if a girl is going to fit in with your family, and of course the same applies for her.
