I read all the Trevor Thom books cover to cover when I did my PPL. I did all the PPL exams at my local flying club, and paid for one on one tuition with the clubs ground school instructor before I sat the exams. I passed all PPL exams first time no problems and that has proved to be an excellent building block as I have worked through my ATPL exams.
When I got out to California to do the flying they asked me what books I used for ground school. Trevor Thom rubbish they said, to much detail, too boring. So I think some of what was said earlier in this thread may have some truth to it. Certainly there was very little in PoF ATPL notes that wasnt in Trevor Thoms book, except for high speed flight obviously. The quality of flight instruction I got in California was good though, I had an excellent instructor.
What I have done everytime I have gone flying on my PPL is get out CRP 5 and calculate wind corrected headings, TAS, expected fuel burn, and updated ETA's and heading in flight etc etc. When it came to the Gen Nav exam that was a big big help I think. 1/60 rule etc etc. They way I looked at it the more CRP 5 questions the better, as I knew I would get them correct.
With the regard to the form of the earth type stuff, I think the biggest thing people struggle with is having spent their hole life looking at mercator type wall maps, school atlas type projections. Hence they struggle with things like convergency, earth conversion angle and so on.