The Lazy/EZ loop is probably the best intro to Moab mountain biking that you can find. It has a little bit of everything from slickrock to singletrack dirt.
This trail has a lot of history and interesting things to see in addition to some beginner to intermediate riding. Dino fossils, slick rock single track and old west relics.
Porcupine Rim was one of Moab’s first backcountry rides. Today it comprises the lower section of the Whole Enchilada. This trail is still a must-do for any MTB rider.