Driving in reverse is the traditional way to get brakes adjusted, but it may depend on how the adjusters work. The Xj manual says you should go back and forth, making full firm stops in each direction. I suppose reverse alone will do it too, but you can get it done faster in shorter space if you go back and forth.
If you've just put in new brake parts, check that the curved cable guides are properly seated in the shoe. The replacement parts have a very shallow protrusion on the back, and fall out easily when you're assembling them. Once they're seated, and the springs are in properly, they should stay, but it's also possible to put the spring in even if the guide is slightly out of the hole, and that will cause the cable to be too slack to work.