I'm starting A-Level physics next week, I got an A* at GCSE. It is my favourite subject and I've always done well in it but I think the most important side of it is the maths. No matter what anyone tells you, GCSE physics is easy- you don't have to know anything, you just have to remember it. If you're good at maths then you can work out any of the formulas you'll be needing, for example if you're asked to calculate the speed of something and you didn't know the formula, you can just do:
Speed is given in mph
Mph = m/ph (miles per or divided by hours)
So speed is distance divided by time
You do get the formulas in the exam though, so this won't even be an issue (just a tip in case you forget one). If you're good at maths, then you'll be good at physics- at GCSE, it's just sticking numbers into a calculator and reciting facts.