In the fall and winter, many pests seek warm places to make their homes. That usually means in your home. Mice have already started to move in, as have box elder bugs, Asian lady beetle and cluster flies which are all over-wintering insects.
The best way to prevent over-wintering insects from entering your home is exclusion. Take a look at windows, floor sweeps and garage doors and make sure they are all seeled up.
Anywhere there are conduits and spickets for water, you want to be sure that there is no more than a 1/4" gap for mice and even smaller for insects.
Steel wool is a great temporary fix, short term. If you have a gap that is 1/4" or more, stuff this in the gap. Mice don't like this on their teeth and they won't chew it.
Most people think that when the cold weather comes, the mice start to come it. But, the mice are already starting to come in. Mice start to move in around late August when evenings start to cool. By the time December and January move around, they are already in. Now is the time to get rid of them.