Idon't know what im doing here... (New Here)
 

i bought a 89 2.3L N/A Mustang Hatch, it's auto. 106k miles
the only mod it has is a magnaflow exhaust with a straight pipe.
I'm trying to get the most mpg out of it that i can.
I plan to remove air silencer, add a k&n cold air intake and remove back seat.
what else can i do to improve my mpg?

my little story,
i bought it and filled it up with about 33$ but it wasnt completely empty but i think a good 35$-40$ will fill it up. i drove about 100miles on the freeway and 65-70miles on california beach street lots of stopping and going and 100miles going back on the freeway.
when i got home i looked under the hood and saw a leak, it was water. leaking from the water pump. so i took it to the machanic and it turns out the spark plugs where real messed up aswell. so he fixed that and fixed the timing belt and the water pump. hoping that can get me at least 300+miles on a full tank.
what are some free things i can do and some things i can invest in that can help.

thank guys. im sorry if this is the wrong section its all a little confusing still ;)

Top of the page there's a list of mods and a list of tips.

dont add the kn intake.
do the list first.

Yup.
The list is on the "EcoModding Central" main page, at the top like Frank said.

First thing, get the tire pressure up where it needs to be. That must be on the list somewhere!! It's free, and quick/easy to do. Will help mpg, all other things being equal.