There's many ideas to save petrol, but which is the most effective? As a starting point, my Magna TS consumed 16L/100km of petrol in city driving. After some months of experimentation with different techniques, I found that the most effective method was (taa-daa!) … to accelerate and brake moderately. Many other techniques (e.g. leaving appropriate space behind the vehicle in front, drive smoothly) are a consequence of this one. Now, my fuel consumption is down to 12L/100km.
Of course, your mileage may vary!