Hi guys, I've not been around for a while and haven't been fishing for equally as long

I have a boat booked for Saturday with a friend. We are going to Grafham and I wonder if anyone can tell me what flies I will need in my box? mrtrout has already suggested sedges to me so I will be finding a step-by-step and tying a few of those but I wondered what else would be worth taking at this time of year. I haven't been fishing since April/May so all the flies in my box are maybe the wrong ones for this time of year?
Also, I've never fished a dry fly before - how do I do it? I know that is probably a really stupid question but I'd rather look silly now than when I'm on the boat.. Do I cast and retrieve or cast it and leave it for a while letting it float about?
Finally, any tips specific to Grafham? I've never been before although I think my mate has been once.
Sorry for all the questions! Thanks for any replies!
Jimmy.