Good luck on this. You're going to need it. Best thing you can do is tune it up as best you can, and have a light foot. Stock estimated mileage was 12 mpg, and its damn hard to get an engines mileage better than it was new 25 years later.
haha..you said "improve gas mileage" and "FJ55" in the same sentence... I can only offer the obvious solutions... tune up, timing, adjust carb, check for vacum leaks..etc etc caveat: If you own a 55 gas mileage shouldn't concern you..
