how to get better gas millage on a 08 suzuki sx4 sport

Turn your car off at traffic lights, do not idle in the parking lot/driveway, do not go through drive through fast food/bank, anticipate red lights and stop signs by letting off the gas early, accelerate lightly from stops, make less left hand turns.
Keep tire pressure least at 30 PSI, change your oil and air filter on time, remove excess weight/junk from the cargo area, use 87 octane gas instead of more expensive high octane versions.

SX4 is one of the higher fuel milage cars out there and there is nothing you can add to the car to improve milage. It all falls on your driving habits and type of fuel you use. Maintain tire pressure at 35-40 psi and drive like a granny :)