You've spotted a mouse or seen evidence such as rodent droppings or holes in the back of cabinets or along walls. Whether you want to simply capture a mouse humanely and release it somewhere else or catch the mouse with a lethal trap, these hints will help you design the best ruse.
Bait and Kill
There are three main types of lethal traps: an empty one you bait yourself with a bar that snaps shut on the mouse, a glue-board style designed to catch the mouse while it walks across it, and bait with a kind of mouse poison that kills the mouse slowly. They each have an appeal, but the latter method leaves you open to the unfortunate circumstance of a rotting mouse somewhere hidden in your walls or basement. The glue board sometimes isn't sticky enough to trap the quickest of mice. Try the snap-trap first. Properly bait the trap with a very sticky, sweet substance. A very small mouse may not trip the bar on the trap unless it spends some time there snacking, so you need the bait to be gummy. Contrary to popular opinion, cheese is not normally a good choice of bait unless it is very soft cheese. Peanut butter is an old standby. If you find it doesn't work the first time, try chunky or creamy and mix some honey into it to increase adherence to the trap and appeal to the mouse.
Catch and Release
There are many so-called "humane" mouse traps, in which the mouse is not killed but is rereleased into the wild at least several miles from your home. The best bait to use with these traps depends on its structure. One such mouse trap consists of a bucket with a 2-by-4 and some bait at the end of the piece of wood, hanging over the mouth of the bucket (see Resources). This could be easily homemade but one version of it can be purchased as well. The mouse falls down into the bucket and remains there until you capture it. This trap can have any bait that smells delicious to the mouse, since it is only necessary to tempt the mouse up to the bait, not keep it there as with the lethal snap-traps.
A variation on the bucket method that might save more space indoors involves a toilet paper tube and a trash can (see Resources). The mouse might come into contact with the bait using the tube method, so choose a bait that is sticky so it requires the mouse to stay longer at the trap.
Another simple and humane mouse trap uses a regular plastic soda bottle and a block of wood (see Resources). Again, this trap can use any kind of strong-smelling bait, even a cotton ball soaked with a scent like vanilla extract rather than food, which might attract ants or other pests.
Cleaning up after the mice are gone is an important preventive measure to keeping future infestations at bay. After you are certain you've caught all the mice, dispose of the dead mice properly, bagging their bodies and throwing them in the garbage or burying them in your yard. Clean your floors, cupboards, lower walls and any area you can reach where the mice touched. Get down on your knees if you have to, but discover every last hole you can find and patch it with spackle, copper sheeting, steel wool or some other method.
Never try to trap a mouse inside the walls of your home, whether by patching its holes while it's alive or by setting a trap where you can't easily get to it. The dead body will rot, infiltrate your vent system and potentially pose a health hazard. It may also attract other unwanted visitors such as roaches or even rats.
The bucket-and-2x4 method can also be set as a cheap lethal trap, with either poison at the bottom for the mouse to eat or a few inches of water in which it can drown.