Hi stinkingbishop and lucky you to have this to look forward to. I envy you! I did an Arvon course earlier this year and it was fantastic. I recommend it 100%. I was unsure what to expect and like you I didn't know what I should have done beforehand or how it would be. I took some stuff I had written (just short pieces) but in fact I didn't really need it beyond the first day, as the input from tutors, daily exercises and workshops plus time for actually writing while you are there allow you to produce so much new fresh stuff during the course that it's like a great big rocket booster for your creativity. My experience was that the tutors take you where you are at (bad English but hope you know what I mean) and you set off from there.
I had a vague plot outline when I went, with loads of holes and unable to get started in any meaningful way. During two brainstorming one to ones with a great tutor, I realised how vague it was and felt very amateur...but in those two brief discussions I shot forward miles, just from having someone experienced to help me to focus on making some key story decisions, and also to tell me that I could write and why didn't I just get on and do it. I gained so much impetus to move forward and some self belief. I came home and wrote a first draft in a month! (Haven't dared re-read it yet...)
It's hard to describe how Arvon works as there's no set formula but I've never heard anyone come away saying it wasn't a good experience. One aspect is being with like minded people in an environment where you can focus on writing, in an enjoyable rather than terrifying way, with no other responsibilities. Enjoy!
It's November - so plenty of time. Ignore friends and family. It's your personal journey.
Also writing does not necessarily have to be about a novel. People are obsessed with writers having to have written a book. Believe me, there are some bad books out there! Better one perfect short story!
Just have fun between now and November. Write what and how you want. If there's a book bubbling then spill it - but enjoy! How much writing have you done before?