I agree that fuel management is something that woofully inadequately taught on the PPL, in fact when I look back on mine I dont think they spent more than 5 mins on the subject! It was only when I really started flying regulary in the club/group atmosphere you start to pick up on things and supplement your PPL - as keeps getting said "Its a licence to learn"
I like to keep it simple so hence the clock face approach, I think doing it every FREDA check is a bit excessive but it works for you then stick with it. You also dont need a fuel flow meter, just look at how many litres they put in on your return and you can easily work out your gallons/hr, again keeping it simple, not 100% accurate but good enough.
Leaning again is something I really got my teeth into post PPL and I think something which wasnt stressed enough on my PPL. A mate (from our group) and myself did an experiment in our PA28, 2 flights upto about 4500, first without leaning and second with. We got from 11 USG/hr down to 7.8 USG/hr, so quite a saving on a long trip and also quite a range improvement (hate the phrase "mission capability" - makes it sounds like I am going to bomb someone
). These are approx figures as we worked it out from the uplift of fuel back on thre ground, but as pay a dry (not wet) rate for the aircraft its all money that stays in our pockets not Mr Browns.
My 2p worth.
J.