One of the many practices used for preventive pest control is exclusion. Exclusion is the practice of keeping the pests out by physically blocking their path of entry.
The pictures below will help to illustrate:
The first picture is of a separation between a door frame, and the brick siding of the home. This opening was large enough to allow many types of pests to enter. Blocking such entries will drastically lower the chances of having pests come inside your home. You may not find all the holes and cracks on the first try, but each one you seal, will be one less entry, and help you to discover others.

The next photograph shows the caulking process at the beginning.
The final picture in this series is the finished product. It will prevent pests, and keep cold air out. It can be painted to match the brick, or the door trim if needed.
