Hi Tulips - have carried out dozens and dozens of Form Fs for prospective foster carer over my 30 year career in social services (now retired) I agree with everything that the posters have said, especially about not looking for Mr and Mrs Perfect (don't think they exist but you know what I mean) The only useful thing I can add is that you must trust your assessor because they are not looking to catch you out/ask trick questions. It is all about the things others have said on the post. Don't look upon it as a question and answer session, it is a discussion, and everything that is raised will relate to the fostering task. How you were parented is very important as is how you parent your own children of course.
Also remember that this is a 2 way process - they are assessing you but you also need still to be thinking of anything that is bothering you, and discuss it with the sw (the prospect of allegations against carers) is the main one, which is not surprising. Often people are worried about the effect on their own children, which again is quite natural and should be discussed. Don't smile and nod and pretend you understand something when you don't - the sw may not be explaining herself/himself properly.
It isn't so much about the detail of the complications in life though of course you will need to talk about that, but as someone said the important thing is how you coped with it, because fostering can be stressful, and being able to highight a difficult patch in your life and getting through it, is all to the good.
Don't tidy the house too much - not cluttered obviously but I always felt happier when the house looked lived-in.
You will have learned a lot on the prep course and I always started asking them about the course and if there was anything that came as a surprise, or bothered them in any way. I was less sure about people who claimed that there were no surprises - it was all fine!
I honestly think the most important thing that foster carers can do to prepare for fostering is to learn about attachment theory (there are loads of books on Amazon) because most of the children coming into the LA system will by definition have insecure attachments with their birthparents, and this can give rise to a great many difficult behaviours. Some LAs run course on attachment theory and I would ask the sw about this. She should be very impressed that you know how important this is!!
Finally, most of the people I have assessed said at the end that they had quite enjoyed it, because ordinarily in life, we don't sit down and have someone "take us through" are life story. Oh yes and please be yourself!!