Make sure your flight computer skills are up to scratch - that's where the marks are, and it will be in your hands the whole exam. It is possible to pass without dealing with too much convergency, but you won't pass without the whizzwheel. And the flight computer questions won't be as simple as finding track and groundspeed - expect some conversions from magnetic to True and Compass to make things fun!
The principles of Navigation are also covered in Flight Planning and Radio Nav, and possibly Instruments with the INS. The General Navigation exam should be looked up on more as a maths exam with navigation as a backdrop.