A-level physics is more or less a continuation of GCSE. There's an element of 'what we said at GCSE wasn't quite true, it's actually...' (and this would be repeated if you ever did a degree, and a postgraduate qualification - physics is a series of approximations). The main tip is to write up the practical elements as soon as possible, rather than leaving them for later. The maths isn't hard - A-level physics will still talk about the acceleration due to gravity on Earth being 10 metres per second per second, rather than 9.81etc - and it is all interesting stuff.
If you can, and you don't need it for anything, drop the chemistry instead. That's much harder and very different to the GCSE.