To get ready, wash the mud off the bottom of the jeep and off the rear drum brakes on the inside face (the side facing inboard toward the dif).
First, you need to adjust the rear drum brakes so that the limited range of the e-brake will work for you. To do this, remove a rear tire and jack up that corner, support with jack stands (not the jack- you are going to have useful body parts under there). remove the rubber plug found on the back of the drum near the bottom. Give the wheel a spin- turns freely. With a small screwdriver and a big one, use the big one to reach in and turn the star wheel until spinning the tire gets tough. Then use the small screw driver to push in on the star wheel adjuster (flat piece touching the star wheel from above), and back off the star wheel just until the drum spins without very much drag. Put the plug back in, done. Do the other side. Somehow, XJs don't self-adjust the back brakes worth beans- hence this manual approach.
Second, crawl under, find the wire cables that come from the drums and meet at a bar which is on a threaded shaft. This is where you adjust the parking brake. Loosen the lock nut, and screw the bar forward to take out the slack (parking brake OFF) .