Just wondering roughly what people are getting in the fuel economy average?

When I first got my 380 the first tank after a while was saying 14.8L/100km
I know have been behaving a little better and put in a K&N Airfilter and now dropped it down to 12.9L/100km. This is with the majority of driving going from Morphett Vale to Wingfield then back each day in peak hour traffic.
Is this normal or not so good and is there and cheapish way to make it a fair bit better?

Cheers,