K I got A* in Maths and Further Maths, and A in Lit and Physics.
For Maths, as everyone else has said, just do loads and loads of past papers. Also make sure you know what is on the spec, because something may not have come up in many years, but if it's on the spec it can be examined.
For physics, the CGP book saved my ass, along with the topic notes for each unit on Physics and Maths tutor. I would imagine there is something similar out there for Chem or Bio, as it is on the Physics and Maths Tutor website.