I know its not the easiest thing to get your head round but grid nav actually isn't that bad. Understand that we are only talking about polar stereographic charts and that the grid heading is given to compensate for the massive variation shift and change in convergency, so we fly a gyro heading which remains the same regardless of what your magnetic compass is telling you.
I found drawing accurate (ish!) representations of the Earth from the relevent pole helps. The Bristol Groundschool notes are fairly good on this, though they do give some slightly complicated examples that you are unlikely to see in the ATPL exams.