I've prefixed your thread so it will show up in the Seicento section the guys in there will be able to give you a much better idea of real world MPG etc.
Also you'll need to provide a bit more info such as age/ engine / model etc
It will depend, as much as anything else, on driving style, type of driving and driver competence.
So, really, while we might be able to tell you what the car ought to get (if we knew the traffic conditions) we'd have no hope in hell of guessing what you ought to get.
A marginally crueller person than me might argue that anyone who worries about fuel consumption in a Seicento should either get a life or take the bus.
Then why not ask something like: "My fuel consumption appears to be heavy, what could be causing this?"
Define heavy!
Define the road conditions!
Get an accurate record of what your fuel consumption is: fill it till the pump clicks off, re-set the trip, drive 20 or 30 miles, refill till the pump clicks off, do the calculations.
You'll find the manufacturer's figures on the net, but the fuelly ones are probably a bit more realistic.
Most common cause of heavy fuel consumption? Stuck open or missing thermostat (car takes ages to warm up), short trips, binding brake(s), holes in exhaust (etc.), over-use of brakes, holding on to lower gears, heel and toe downchanges at every traffic light..........
On a Run i can get High 50s , but lately ive been getting low 30s , just the way ive been driving , but mine is Quite modified , so that will be affecting it a little