This is the time of the year to cut everything back. Shrubs like lantana, trees that have not already trimmed (tree trimming can start in November) and any perennials that need cutting back. In the desert this is the coolest time of the year so anything that is going to go dormant will be most dormant now. The only shrubs that should not be cut back are are shrubs like bougainvillea, tacoma or ficus which really are not desert plants and are frost sensitive. These can be cut back after all risk of frost are over. By the end of February most plants will start growing again.