My jeep burns too much gas

i have mistubishi mentro 1997. it runs 10 miles per gallon

Don't push so hard on the gas pedal then!
Take off gently and let the other idiots race away at the lights.
When you see a light on green in the distance don't race up to it 'cos you ain't gonna make it, ease off the pedal altogether and just coast up to the lights, they'll probably be green again by then. Do the same thing if they're on red.
If it is genuinely a mechanical problem then take it to a mechanic but the above advice is good for all occasions.

The 1997 Mistubishi Montero is rated at about 14 MPG city and 18 MPG highway. That's a new vehicle, tuned and timed. I wouldn't consider a loss of 4MPG on a 13 year old car as being abnormal. Changing filters, plugs etc. might help a little but the best improvment you could hope for is 4 MPG.

http://www.fueleconomy.org/feg/bymake/Mitsubishi1997.shtml