Looking for advice from anyone currently on the nat sci course as to what I can do to improve my chances of an offer.

I'm currently in Year 11, about to take my GCSEs, and am hoping for very good grades across the board, for my A-levels I have chosen physics, chemistry, maths, further maths and design & technology, I am also trying to arrange taking a GCSE in astronomy and some qualification of computer science. What I am looking for is advice about what extra things I could do, to give myself an advantage over other candidates when it comes to applying for universities, such as courses, further reading or anything I could do and put on my applications.

Thank you for your help and your time in advance,

EDIT: Also I would find it helpful if you could comment on what you found were the more difficult areas of your studies from A level to your current level, I'm hoping to head towards astrophysics type areas.