Tyres is a good starting point, inflated to the correct pressure but also what tyre is it, I did a comparison a while ago & the weigh between brands differs significantly Michelin & Goodyear tend to be the lightest, with conti being the fatty, tyres rolling resistance plays an important part in your fuel economy.
I've being driving my stg2 R wagen up & down the M1 recently & just by sticking to the limit I have managed to achieve some crazy mpg figures for a 400bhp car .
Last week Wakefield to Nottingham I managed 42.8mpg, & having done 90 miles already it was still showing 380 miles range, boring but economical ;-)