E23 Fuel Economy - Am I doing something wrong?

I've had my E23 for a few months now and I'm consistently getting around 12mpg in mixed driving. My last tank was on a mix of urban and motorway driving, with a few spirited country roads thrown in. The rest of the owners seem to be averaging mid-teens, and some even higher, so I'm starting to wonder if there's something I can tweak to get better fuel economy out of my 530i.