hi!
im assuming you're starting year 12 and not year 13?
if its y13 sorry this won't help 😭
I have almost finished my first year, and I have chosen the same subjects as you.
something I recommend highly is, not to fall behind at all, on the first day make sure you have a way of taking notes and keeping them organised etc.
from the first day make a good relationship with your teachers so you always feel comfortable enough to ask them for help, which I promise you, you will need a lot, these subjects together are really hard.
don't overwork yourself or you will experience burnout pretty quickly and then exams will be much more challenging to manage, don't worry too much about the exams you do in the first year, even if in June/July next year you still struggle, over the summer holidays you can revisit all of the first year and be ready for the mocks in the second year, as these grades will go to your predicted grades for university.
if you feel you're really struggling get a tutor asap, if you cant afford etc then talk to your teachers about it and they could sort something out for you!
overall, work really hard from the start as it is a big jump from your previous school years, but you should also absolutely have time for yourself, find a hobby to maybe add to your personal statement or just for time to relax like art, take lots of breaks between studying!!
hope this helps, good luck with alevels!! (:
btw what are you thinking of doing after alevel?