Mouse proofing your home or business is all about being a good detective. The pros call it exclusion, and it can be pricey if you hire a professional, but if you have an eagle eye and some steel wool, you too and be an exclusion expert.
Starting in the basement or crawl space, turn out the lights and look for daylight. Look along the top ledges, around where pipes and wires enter, around the corners and where the electric panel is located. If you can see daylight then a mouse could wiggle its way in.
Next check out your garage. Shut off the lights and if you see daylight then a mouse can scurry under the crack. Same with your entry doors. Level these areas or put a door sweep to keep mice out.
Other areas to concentrate on would be missing mortar from your brick wall or stone foundation, areas up high where cables enter, the soil next to the foundation. Mice can be resourceful if they want to enter a home and if you work to keep them out you will be doing yourself a big favor.
Some products that work best for exclusion are steel wool and cement. The foam is ok, the one problem is that the mice can chew through that easily. The good thing about foam is that if you noticed a mouse has chewed through the foam, then you know that is definitely a source of entry.