I think pre-planned fuel circles make perfect sense if you are flying a high performance jet on a low level NAVEX where things happen fast and wind has a relatively small effect on flight time. They IMO make no sense in the context of a PPL flying your average Cessna or Piper.
From the very first lesson I teach my students to think about fuel as "time in your tanks". This of course starts with what the dipstick shows on the preflight. Lessons which are flown in the local area use a block fuel burn (ie a conservative average of what is typical for an average training sortie, which is usually about 20 % higher than the leaned cruise fuel flow in the POH), giving the time available in the air for that lesson. This time minus the reserve is the "we have to be on the ground no later than" time.
Navigation exercises are planned in the usual way but I insist that the student be able to tell me how long they can fly from the top of climb point. Have to go somewhere else from any point in the flight ? Well after you figure out how long it is going to take you you can ask yourself "do I have that time in the tanks". This is really useful when you have a GPS (which IMO is mandatory equipment now) because you can get instantaneous ETE information to anywhere (obviously to be double checked early for any GS changes caused by changing your heading)
As for fuel gauges, I intensely dislike the blanket assertion that "fuel gauges are useless".
If you go to the POH for any Cessna there is an equipment list that specifies what equipment is "required". On that list is fuel gauges. If you are flying a Cessna and the fuel gauges are not working then the aircraft is not being operated in accordance with its type certificate.
My experience is that light aircraft fuel gauges particularly the ones in Cessna's are not particularly accurate at the top of the travel but once you get to 1/3 or less quantities they actually are pretty good. If you own an aircraft it would seem foolish to me not to calibrate the gauges by draining the tanks and filling them in 5 gal increments.
Unfortunately if you are renting some beater from the flying school you do not have much control over the state of the gauges but you can still get a feel for what they are saying by comparing the dipped amount to what is showing on the gauges. This simple check is almost never taught in flying schools. If you are filling the aircraft with full fuel after your flight, before adding fuel estimate what you think you burned and compare it to the pump meter.
If it is your own aircraft or a rental where you usually fly the same aircraft, with a bit of experience you can get consistently pretty close.
