Maths should be simple. If you're doing edexcel, C1 is piss, just do a couple of practice papers. With C2, do practice papers and also go over the theory for slightly awkward stuff like area under a curve in segments to make sure you're getting it right. IF you're doing S1, it's all about putting numbers into formulae, but I suggest going over discrete random variable, probability and the definitions. Again, practice papers. If you're doing M1, practice the last questions on papers, they test you on Statics, connected particles, suvat and everything in between. Make sure to go over moments as those can be tricky too. Hope this helps!