The best fuel system/guages are in the Yak 52
in it's original form it only carries 120 litres, the 2 wing tanks drain at the same time, so no fuel selector. Each tank has a row of lights. From memory they are at 5L intervals. They are very accurate and the best thing about the yak is that on average it burns 60L/hr so the guages tell to your remaining endurance
In other planes, i work out how many minutes of fuel in each tank, write the time i select each tank, and when i finish with that tank i write down the new endurance for it, always trying to keep 45 minutes reserve in one tank