Fuel Conservation Or Tips

I have a 2001 Maxima with 40,000 and I am getting horrible mileage.

Can someone please tell me some tips that I can perform to get better gas mileage other than

change air filter
change oxgen filter
change plugs (WHICH PLUGS DO I USE, BOSCH PLATINUM + 4 ???/OR STOCK FROM NISSAN (NGK)
fuel filter

WHAT ELSE CAN I DO ?
I DONT KNOW MUCH ABOUT CARS.

THANK YOU FOR YOUR ANTICIPATED RESPONSE

Use the cruise control on the highway. I have over 100,000 miles on my car and still get around 420 miles to a tank.

Energy wasters are quick acceleration and braking.
Avoid both as much as possible.
Proper tire pressure helps.
I have a '93 Maxima and get around 11 km/ liter
or 770 km/481 miles to a tank

Don't press on the pedal as hard. I know that's my problem.