I don't know about Gen Nav - it's one of my favourite subjects - but this is what I did for the ones I did find hard:
Rather than going through and copying out notes word for word, go through your notes (the school notes, not your own handwritten notes) and highlight the important bits. Then go through and write out all the bits you've highlighted, using more than one colour of pen (I use red for emphasis).
I found it worked for the subjects with lots of facts. Gen Nav is more of a practical subject so I think in that case get yourself lots of practice papers and keep practising!
If you're having trouble getting to grips with concepts, don't be afraid to get in touch with Bristol - they're very helpful!
TB