Can I improve my MPG?  The obvious answer is to remove all the heavy stuff from the boot!  Overloading your car with stuff that you don't need to cart around will have a negative effect on your fuel consumption.
Be gentle with the accelerator and the brake!
Find a local tyre and exhaust centre and have them do a free check that the tyres are correctly inflated and aligned properly (examine tread pattern for unusual wear pattern - bad alignment is like dragging the tyres sideways for 20 miles and wastes a lot of fuel).  While the car is on the hoist, have them spin the wheels and listen for scraping, dragging brake pads that can indicate a seized caliper (one dragging pad can cost 2-4mpg).  
Use a good fuel treatment (STP, Wynns, Unipart, Forte, Ametech) to clean the injectors' fuel tank and fuel line etc to get rid of moisture.  
Check the EGR valve is clean and not stuck closed or open. An EGR valve stuck open makes the engine run cold and erratically. An EGR valve stuck closed causes overheating and destroys turbo seals and causes emissions problems.  
Install a new fuel filter (often overlooked but a major problem in high mpg in modern cars and causes many injector problems).  
Check the spark plugs and leads (or injector spray pattern) are ok.  
Find your radio/immobiliser code and then have your mechanic disconnect/reconnect the battery to reset the engine computer, which should cure any over-fuelling problem.  Over-fuelling washes and scores the cylinder bores which increases friction and causes high fuel consumption.
Assuming all the above have been checked and are fine, and assuming also that you have no broken parts in your engine e.g. piston rings, cracked pistons etc., if your MPG is still high it is probably down to a worn engine, and we would recommend 2 small 250ml cans (500ml total) of RESTORE  in a 2000cc engine and this should be enough to return your car to being a tiger in under 500 miles.