ok so power is out of the question. anything i can do to improve efficiency?

i read somewhere about wrapping the exhaust in insulation so the engine doesnt have to work as hard?

would changing the spark plugs have any effect? changing the paper filter for a K&N filter do anything?

i know these are stupid basic questions, i never really got under the bonnet of a car before but its was my brothers car and he was determined to mod it up, now he has gone and the car was given to me i kinda feel obliged to learn this stuff and get my hands dirty.