Inspect the entire house, from foundation to roof, for small cracks and holes that could be used by mice as entry points. A thorough search is necessary, as mice in the attic may have entered on a different floor of the house. This is often the most difficult and time-consuming part of the task but it's necessary to prevent future infestation.
Fill all small cracks and holes with expanding foam sealant. There are two types of foam sealant: latex-based and polyurethane-based. Either type will work for this task.
Locate mouse droppings in your attic and place wooden spring traps where you find the droppings. Place the bait on the traps and carefully set them.
Remove and dispose of the mice carcasses.
Vacuum any rodent droppings left behind with a vacuum cleaner not used for regular household cleaning. For this purpose, it's best to purchase a small, high-powered vacuum with a hose extension, such as an easy-to-carry Dewalt or Shopvac, that can be left in the attic for cleaning in that space only.