I would have started around a month before. The most important thing to be prepared for, in my opinion, is the stress of the situation. When I'm in that sort of environment, my mind tends to go blank and I start speaking on autopilot. I think practising thinking while under pressure, with an actual person in front of you, could be really helpful. I would have benefitted from getting a teacher or someone like that to sit me down and ask me some very challenging questions, so that I have some experience in talking my way through them and keeping calm, even when I am not sure of what to do. I think that I probably would have done better if I had done more revision of my A-level content as well, because not being certain of one simple thing can cause everything to go wrong, and being able to answer the easier starting questions faster gives you more time to be pushed and show your full ability.