I'll admit to being a bit obsessed with fuel economy...am to the point now that I wish I didn't keep track of it. Am coming to the conclusion that the folks around here that just fill their tank when they need to while not doing the math afterwards are better off. There, I said it.
What you can do:
Don't lift it &/or put big/heavy tires on it.
Like Zedbra said, right foot will dictate.
Driving at 55mph-65mph will net you your best economy.
Idling as well as stop&go city driving are the worst.
Assuming you have the V6, just grin and bear it. Torque is king!
The engines on our Frontys are reliable, but old-school. I have a new '16 2.5L KC with 5-spd. At a steady 70 on I95 (which is the posted speed where I live and commute) I have put almost 3K miles on the truck and am averaging 23.5 mpg overall. On the rare occasion I lead-foot it and do 75-80, my mileage will fall to about 22mpg for that tank.
Not much else that can be done, except as others have mentioned, don't bury your foot in the throttle.
Welcome to the site and congrats on your purchase! Post some pictures when you get a chance. A lot of good info here regarding mods in case you are thinking of doing any. Check out some of the garages and you may get some ideas. Safe driving and happy modding!