Need assitstance in improving my cars

Hi friends,

                I own a Fiat Uno Diesel 1.7 ELX AC(2004) and a Zen D PS(2005). I bought the Uno in 2005 and the Zen in 2006. The Uno had a mileage of 15000km and the Zen had a mileage of 12000 km. Now, both the the Uno has crossed the 1,00,000 km mark and the Zen is about to cross it. This is due to my average driving of around 40,000 km a year(50-80km in weekday and 500km on weekends). I am getting a mileage of around 14 to 16 kmpl in the Zen and 12 to 14 kmpl in the Uno. I do not cross 120kmph in the Uno and 100kmph in the Zen due to safety reasons. I would like to know if there is any way of improving the cars’ mileage, power and torque and safety. I would also like to know at what no. of km on the odo will the cars run out of steam and if theres a way of improving it.