If its a bit juicy on fuel, the only way you can sort it out is:
A. Service it:- Plugs, Oil/Filter, Air Filter,
AND/OR
B. Turn on the trip meter, find out how many miles you do with a tenners worth of fuel for example, and then keep an eye on the trip counter so you know how many miles you got left before you have to visit Mr BP or Mrs Esso again. <-- this way you'll stop doing extra miles, and just generally be more careful with driving around for no reason ...