A-Level examboards are more focused on outcomes and less with experiments, but it is not saying that experiments are not important. First, question yourself 'what does this starting point remind me of?' and write down every single thing that goes through your mind - any circular objects, any natural phenomenons that involve circles, any artist who works with circles, and even the philosophical concepts derived by circular forms or given to circles through the history.
From the brainstorm, you have now harvested large amount of options to start with (which medium to use, which artist or concept to refer to). Think about different ways to create a piece, distinctive qualities of different medium, and what it will bring to your work, both technically and conceptually. And start sketchbook experiments.
Please note, that at this early stage, do not limit yourself with one single medium, nor script a very complete plan at this early stage. Open yourself to uncertainties and changes that might occur, and make the most of them by detailed and in depth reflection.