Keep it well maintained--same as always. Fluids, filters, spark, gaskets, sensors, fuel system, brakes, etc--keep them changed/in good shape. Is there anything wrong with it? If it's still running well, what are you worried about? I've seen an article featuring a guy who went over 600k miles on his 4.0, and I've read a rumor of someone hitting 700k. I've seen plenty exceed 300k still running strong.
My 96 XJ is for sale in the event you want something to restore or build into a wheeling rig. Sale ad is HERE