Remove all food from your attic. Many rodents are simply looking for food when they enter your attic. Rather than give them a reason to be there, remove all items that might serve as food from your attic. This might include old Easter and Christmas candy.
Seal all cracks that are at least a half-inch wide. Consider using caulking to seal cracks and fine mesh to cover vents and ducts.
Place traps around your attic. Rodent trap types include live traps and kill traps. Live traps will trap but not kill the rodents. Kill traps, such as poisons, are designed to kill the rodents.
Remove firewood from your attic. If you are storing firewood in your attic, consider moving it outside. Rodents, including mice, like to make nests in piles of firewood.