Go easy on the skinny pedal is the easiest way to improve it! How long has it been since you changed the spark plugs? I went from getting 11.5 to barely 12 MPG's to 13.5 after i replaced my sparkplugs!
2010 JKU - Stock for now
2005 WK - 6" lift, 35" BFG's, a lot more (SOLD)
First, do a search and you'll find many threads on this subject. There are many ways but, as said, driving habits are the biggest factor. Tire pressure is also a biggie. I run 40 PSI in the fronts, and 38 PSI in the rears. Other than that the best way is to increase the Volumetric Efficiency (VE) of the engine. This is done by improving the flow of air through the engine.....mainly intake, head port/valve size, cam timing, and exhaust. With our Hemi's, IMO, the biggest weak spot is, by far, the exhaust system, specifically the small "log" style manifolds. Also, the transmission shift schedule can adversely affect fuel economy. With my mods. (see signature) I get about the same as others in town (~13-14 mpg), but on the highway my range is 20-24 mpg, with a normal of around 22 mpg. Remember these things (4WD Hemi models) weigh ~4800 lbs. without you and any stuff you're carrying. I figure mine, with me, the wife, a full tank of fuel, and camping equipment runs a little over 5500 lbs. In town, the normal weight is the biggest problem......moving the mass from a stop everytime.
Currently I am doing a little test with mine. I went to the drags this past weekend and changed the WOT upshifts from 6000 RPM to 6200 RPM. I was in a hurry and didn't insure my custom shift schedules were still installed and they reverted to the canned ones in the tuner. I've noticed that my MDS works a whole lot less now, and after filling up my FE is down almost 2 mpg, so far. I'll do a couple mileage tests to verify if this continues, and I'll have to return it to the stock tune when I take it in to the stealer for the transfer case actuator recall. That should be real fun then.
06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, K&N Filter, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS Tuner, Cust tubular hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, SRT Reps with 265/45&295/40X20's.
To give you an idea on the lousy stock 5.7 exhaust system, here's a link to the thread I did on the differences between the stock 5.7 WK and LX "log style" exhaust manifolds. You can see that the LX ones are quite a bit better than the WK ones.
Search bar. However the main way to improve gas mileage is to go easy on the gas pedal and try and avoid stop and go traffic. Going 55 mph also is the sweet spot for the best gas mileage. We drive Jeeps...poor gas mileage is a given. At least it's not an FJ or Hummer
'15 JK 2.5" lift on 35's
'06 WK 3.5" lift on 33's (Sold)
On the freeway or rural highways, I get around 19 mpg. Burn a tank of gas on stop and go errands, I end up around 15-16 mpg. I can imagine that true city driving (which I try to avoid at all costs) would really cruch the mileage.