You can improve from 14. I average 16.5-17 mpg with mixed city/highway driving. I get 20-22 on the highway.
1999 Cherokee Sport 4.0/aw4, 5.5" lift, 33" STTs, 3.55 gears, 62mm throttle body, aFe intake, header into 2.5" exhaust with Magnaflow free flow cat and muffler.
Start simple with plugs, wires, cap, rotor. Check all your fluids, change your oil, run some Lucas fuel injectors cleaner through it. Change your upstream 02 sensor. Basically make sure everything is functioning as it should be. After that, intake and exhaust modifications can help a small amount. Doing all of this together will make a noticeable difference.
2005 WK Limited, 5.7 hemi, QDii, aFe intake, Magnaflow exhaust, Taylor shorties, Diablosport tuned
1999 XJ Sport, trail rig, lots of goodies