I reguarly fly trips of about 5 hours and fuel management is critical to the safe compleation of the flight , knowing the exact fuel consumption of the particular aircraft that you are flying is vital if you are going to fly down to the last 30 min of fuel.
You have to set the engine for the known fuel flow and maintain that setting, changing of tanks to maintain the balance of the aircraft is vital as this cuts down on the trim drag.
Changes of fuel tank should be logged by time as the clock is the best fuel flow indicator that you have and there should be no doubt as to the location of the last 30 min of fuel !.
Consider "aft loading" the aircraft because the closer to the aft C of G limit the aircraft is the less trim drag you will have.
Try to climb as high as you can as the TAS wil increase with altitude and may well ofset the head wind , the other thing with flying between 6 & 10,000 ft is that in most of Europe a lot of direct tracks are avalable when crossing controled airspace and this saves a lot of fuel not having to fly around control zones.
Have a clear picture of what you are going to do if you run into un-forcast headwinds and have a plan for on route diversion, this is first a safety issue but for insance an early diversion into Jersey would save a lot of nail biteing over a late diversion into Nantes as well as a lot of money.
Manage your fuel tank changes as best you can to not select a "new" tank at a critical time , 50 miles south of Southampton is not the time to find out that the fuel in the right tank in contaminated and there is only fumes in the left tank.
The most impotant thing is the one most often forgotten PRIOR TO DEPARTUE CHECK THE TANKS YOURSELF , there is no substitute for checking in the tanks with a dipstick, readings from the bowser and calculations of other pilots who have flown the aircraft are not good enough CHECK IT YOURSELF.