I have a ae92 sr5 auto

first car, i wanna get a couple upgrades for it, but nothing too big because it has .. 180 k miles. Any suggestions?
my last fill up i got 210 miles, and the one before that i got right around 300, and right now im at .25 of a tank at 107 miles, so its really random, i would just like to have a nice consitant 300 or so but i dont know exactly what to do..
when i got it (about 2 years ago) i replaced the sparks, rotor, distrib, and fuel filter. I just recently replaced the alternator but besides that, thats all ive really done. Any suggestions?
i did an unofficial 0-60 in 13 or so seconds