taking proper care of ur car will do wonders in that dept.
on a more serious note...anythin that helps the flow, intake and/or exhaust, of the engine. the easier it is 4 the engine 2 output a certain power required, the better mpg due 2 efficiency. its only starts 2 hurt when u start adding things/tuning things at the pt where the engine needs more fuel.
4 example, replacin the stock cat w/anythin (hi flow cat, ORP, race header anythin) usually yields better mpg. i've proven it. had the car stock 4 a while, then used a ORP=better mpg, sold ORP, stocker back on=mpg down, now i'm tryin out a high flow cat=mpg back up.
mind u ur mpg will suffer if u like 2 'try out' ur new found power
-Ult