Mice prevention involves five basic measures. The first is creating a sanitary environment.
The second is removing any food supply. The third is eliminating possible shelters or nesting areas.
The fourth is blocking access into the building. And the last is using mice traps or bait traps.
Mice prevention should begin in the yard. If a yard provides a haven and sanctuary for the rodent, they will thrive and multiply.
If there are fruit trees, ripe fruit should be picked from the tree and fallen fruit should be removed from the ground. The yard should be free of debris.
Ideally there should be no wood piles, yet if there is one is should be away from the house and any entry doors. Remove weeds and trim overgrown vegetation.
Secure trash cans lids and empty them frequently.
Do not leave open containers of pet food, bird seed or garbage in the garage. Mice can easily make their way into a garage and food will encourage their visits.
Avoid clutter and don't use the garage as a pantry. Boxes of cereal and other foodstuff will be an easy target for the mice.
Mice need no more than a 3/8-inch opening to make their way into house. In the winter the warmth of the house might entice the mice inside, and during the summer it may be the cool air.
In either case, closing the openings will reduce the possibility of mice entering. Broken windows should be repaired, missing or damaged weather stripping should be replaced, cracks in the walls should be filled and any gaps around venting and piping should be filled.
Mice can enter a house by the roof. They make their way to the roof by utility wires and trees.
If there are gaps or openings around any air-conditioning units, vents, conduits or water pipes the mice can squeeze through the openings and enter. Repair loose shingles, fill gaps, and make sure the spark arrestor on the fireplace chimney is secure.