In summer it is difficult to shut off engine while waiting on signals or during a traffic jam and this exactly ruins the milage no matter ac is running or not.
Try shutting down the engine on a pleasant night or day during summer and make it habit during winter to shut engine on signals where you know when your turn will come or while waiting in long standstill queues at crossings and then see the magic.
Even in winters I see people pumping gas to warm up engines on idle which is total waste of fuel. Once you start the engine in winter 10-12 secs are enough and start moving slowly at low rpms it warms up the engine faster while you also travel some distance which improves your final fuel economy.
Also always have a tank topped up when u go for refueling. Mark the good fuel stations in your area or on the way to work. If u are little bit careful you immediately know which pump has done hanky panky.