Make sure your personal statement conveys your interest in the subject – write down talks you’ve been to (and what they made you think), open days you’ve attended (and what you took away from them), and maybe even books you’ve read (and whether or not you agree with the author and why). Are you seeing a common thread? It’s less about what you’ve done and more about what you make of it! It’s best to only mention one book or one talk, but really go in to some critical analysis, rather than to just write a list of seven without any additional commentary.
Any extra-curricular activities should be ‘super-curricular’, i.e. related to your degree: for Maths, maybe the Maths Olympiad, for Science, maybe a Science EPQ or that time you entered a Lego competition (totally relevant to Engineering!). For Law, I talked about teaching and debating, and the self-discipline involved in teaching myself a language as an A Level. You can honestly make anything work – try to make yourself stand out a little by having something people don’t normally have! But don’t worry about not having twenty different hobbies – you don’t have space to mention more than one or two, and you won’t really be asked about your personal life at interview.
What I would reiterate, above all, is to not stress over the personal statement. If you’ve spelt everything correctly and you’ve got all your proof that you’re genuinely and voluntarily interested in your subject outside of school then you’re doing it right! And, to the year 12s going in to year 13 – for the love of all that’s holy, take a few weeks off this summer. Breathe. Let yourself detach from the intimidating university admissions process and the pressure of A Levels for a bit, because that will let you be so much more engaged when you jump back in.