Now is the time to start planning your strategy for bringing your houseplants inside for the winter. Moving your plants inside early in September (before temperatures dip into the low 40s and even into the 30s) is what keeps the leaves from falling off of the plants. If you wait until late September, or even into October, you can be sure that the leaves will turn yellow, then fall off. It's all of those cold nights that "harden-off" your plants and when you take them inside, they collapse. The "shock" isn't caused from the move, but from waiting too long to do it.
There are some plants such as hibiscus and mandevilla that I would rather have the leaves fall off, in fact, if they do not fall off on their own, I will pull them off. Taking off the foliage before bringing them inside will ensure that I am not bringing insects and insect eggs into the house. For best results, remove the leaves then spray the bare stems with a soapy water solution followed by pouring more soapy water right through the soil. This chases away bugs that live in the soil. Do this in October or early November...no hurry.
Most hanging basket plants are simply thrown away at the end of the season but if you want to try and winter them over, generally it is a good idea to trim them back, almost to the edge of the pot. Place your plants in a sunny location close to the glass so that they will be a bit cooler then if placed away from the window and stop the weekly watering. As we get closer to fall and winter, allow your plants to get fairly dry between waterings. Only water every 10 days, and later on, as we have shorter, gloomy days, only water once in 14 or 15 days. In December, January and February, only water once a month. But remember, when you do water, always water thoroughly. After cutting them back, spray the remaining growth with soapy water.
Most of your outdoor perennial plants need to be attended to also, but not yet. You should really wait until a couple of good frost hit your plants and damage the foliage. This frost triggers a signal to your plants that winter is coming and helps to slow down the growing process. Other ways of slowing down the growing process is simply "no more pruning", or cutting back your plants. Trimming stimulates new growth and during the early fall that is not a good thing. So don't even cut off the dead flowers until late November, even December. And starting right now, "no more fertilizer", except on your lawn. If you must fertilize, use either bone meal or slow release garden granules. Even the plants that you took into the house should have fertilizers cut back to half strength, and only once every 6 weeks or less through the winter months.