Probably the most asked question right now is, "Can I cut back my rose bushes at this time?" and the answer is, "No!" In fact from now until Thanksgiving nothing should be cut back with the exception of your lawn. When you cut back plants, it not only makes them look neat and tidy but it also promotes new growth, the one thing that you do not want just before winter. So if neatness is what you are after, fine, but wait until cold weather is here to stay, i.e., Thanksgiving.
Summer blooming perennials with tall, dead flowers sticking up out of the main plant may be cut back, just don't be in such a hurry to cut the plant itself back until later. Good examples of this would be hosta or daylily plants. Take off the flowers but wait a little longer before cutting back the foliage (the leaves). However, later it is imperative that you cut back the leaves as the freezing temperatures will turn them into a rotten mush. This could be a good time to do some division of many of your perennials as dividing and re-establishing these plants give you a great head start into next seasons growth. In this case, you need to get on it immediately.
Fertilization of any plants other than your lawn is a very bad idea in the fall. It is basically too late to "fix" plants that are having trouble this late in the season. However, top dressing around your plants with composted materials such as cow manure, then mulch...and, or the use of organic material such as bone meal is probably beneficial to almost all of your perennials including shrubs and trees. This is your gentle way of helping your plants get better prepared for next spring. Also, make sure that by November your plants are not in a state of drought. Usually plants that go into winter on the dry side, die. If it doesn't rain much in October, you may need to water your plants one last time before the end of October.
In order to lock in the moisture for the up-coming cold, windy winter, it is a good idea to use a product such as wilt-pruf late in the season. It holds the moisture in place to keep your plants hydrated and helps to prevent dried, burnt looking needles on your evergreens. This product, and many others just like it, can be found in a ready-to-use trigger-action spray bottle for small jobs or a concentrate that can be mixed and sprayed for those larger areas.