Work leaves into growing areas. If the leaves are shredded first they are easier to rototil, 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.
Shred all dead annuals. After they are shredded, they can be worked into the garden or flower beds. The lawn mower works well for this too. Be careful of annuals that reseed themselves, though. They can become weeds in a garden.