Mice can basically nudge their little noses into the hole the width of a pencil. SO the battle to try to keep them out is long, but can be accomplished. Start with the obvious areas. Take a walk around your home and look for wires and pipe that enter your home. Can you notice any space around the wires or pipes? If so then you should caulk around these openings. Next place to look is the exhaust of your dryer. Often times lint props the flap open leaving a clear highway for rodents to enter your home. Others areas include under the garage door and entrance doors. If there are gaps then they can get in. Make sure all the weather stripping is in tact. Lastly, if you notice any cracks or holes in the foundation of your home along you outside perimeter then cement those areas up.
Happy fourth of July!!