Ornamental grasses add a lot of winter interest to the yard so please refrain from cutting them down in the fall. Come spring you can cut them back to about 6"-8" in height. If the centers of the ornamental grasses have died out, be sure to dig up the entire grass clump, divide it and then replant it. Miscanthus grasses are notorious for dying out in the centers so be sure to watch them closely.
Perennials will perform better if they are not cut back in the fall. The dead foliage actually provides protection for the crown of the plant. Many of them like echinacea also provide winter interest. If you need to divide perennials, the fall is the best time to perform that task.
Be sure to also mulch shrub roses so that the crown is protected, and then be sure to remove the extra mulch in the spring so that the plant can grow and flourish.
Also winter water your trees and shrubs especially when the snow fall is sporadic and the snow does not have much water content. You should provide moisture to trees and shrubs once a month during the fall and winter to prevent desiccation.