Do not pile wet, fresh clippings more than an inch deep at a time or they will turn into a stinky, sticky mess. Shredded leaves in the fall can be used as a mulch around the trees, shrubs and perennials. By spring, the leaves decompose and add precious organic matter to the soil. Leaves can be shredded by running over them with a lawn mower. This is usually easier that raking them up, even though it makes a lousy leaf pile for jumping.
Work leaves into growing areas.
If the leaves are shredded first they are easier to rototill, but shredding is not required. Adding some nitrogen into the area will speed decomposition. Use evergreen needles for mulch or a soil amendment. They will acidify Utah's alkali soils while increasing the organic content. Conifer needles break down slowly but still improve the soil over the long haul.