After having kept Swift DLX for 4.5 years and driven over 110,000kms including a couple of Pakistan trips (KHI to Nathiagali) in it, here is my feedback on the matter:
1) In-city driving, with a light foot, air pressure 29/29, and with ADVAN dB Yoko tyres, the max I get is 11km/litre;
2) On-highway driving, same tyres, max I have gotten, was 14.5kms on a 4,500km trip;
Following steps will help you get the above-mentioned 11km/ltr mileage within city:
Weekly cleaning of air filter, radiator and AC grill as well as cabin filter (behind glove compartment) helps improve fuel economy;
Increasing air pressure to 33/31 can bring your in-city fuel consumption up to 12.5 km/ltr, but that would be at the expense of a bumpy/bouncy ride;
Personally, my fuel efficiency has been better with ND Iridium spark plugs as compared to NGK's normal (stock) plugs;
Fill your tank with TOTAL fuel and stay far away from PSO. Based on lab test results carried out in 2008/09, in Pakistan, TOTAL fuel is the most refined and hence fuel efficient, after which comes Shell, then Caltex (recently acquired by TOTAL) and last comes PSO;
Also get your ECU settings checked at one of the better 3S Suzuki Dealership near you and ask the technician to check whether the configeration is optimised for optimal fuel efficiency.
Hope the above helps improve your fuel efficiency.
In my personal opinion, at the moment, among all the PKDM hatchback options available, the Swift offers great value for money and balances comfort, reliability, exterior looks, interior and features. For the price (Rs. 1,088,000) I paid for my brand new swift back in 2011, I think I've gotten more than my money's worth. And with me waiting for the Civic to be launched in July, I'm still thinking about keeping this Swift as a second errand-car.