Hey~
As a current VA student, I would definitely suggest you to start early - preferably by the summer holidays. From my experience anyways, although it's important to work on your concept, there is only so much you should do before you just start and stop worrying about all the what ifs. Personally I started in around term 3, which was really dumb, because I'm rushing my work now seeing as it's dued this week. Keep in mind that although it's great to have everything mapped out - (and you really should, since art is an expensive subject) your major work will continue to change throughout the year and may end up not what you initially envisioned it to be. So, as someone who spent far to long on planning, I would definitely recommend not to dwell too long on the theoretical and more on the practical.
Your concept and technical ability should be refined and sophisticated but you don't worry too much on what the examiners are looking for. They really are only looking for any deep concepts that have been well portrayed. If you've been to Art express, you'll see that a wide range of subjects and focuses are displayed every year, there really is no right or wrong concept - unless if it's offensive or your work has prohibited items in them (glass, needles etc)
As cheesy and overused as it is, you really should do what you want to do. You're going to be spending (hopefully) a long time on your BOW and it's so incredibly easy to get bored of your work. The more your passionate about whatever you're painting, the more engaged you'll be with your work. Don't be afraid to challenge yourself - you have legit a whole year to do this, but don't be too reckless with your experimentation. E.g, if you've never painted with oil, it might not be a good idea to learn this year since oil is a medium which some individual absolutely love and others hate.
Other than that, perhaps ask your teachers about past students work and get an inspiration there - if you have no idea what to do. Or, conversely, go to art express's website and look through the painting/drawing sections and see what the standard for those works are. This will help you set up your own opinion on what you need to do. Your teacher ~should~ be there to guide you through your BOW, so don't be afraid to ask.
All the best! Visual arts can be quite frustrating but it's also an extremely rewarding subject.
