Locating the entrances that vermin, bugs, and arachnids use to come inside can be as simple as taking a walk around the perimeter of your home. Bring a hand mirror and tape with you to inspect the underside of your walls and siding. You'll probably see a few gaps. Mark the holes with the masking or painters tape so you can find the hole later and seal it. If the hole is too large to be sealed with caulk, try copper scrub pads to fill the gap (and then seal the gap with foam).
Most of us have that doorway that is not sealed tightly- you can see the light around the edges. If you can see outside light, then it is an easy entrance for critters. Before the weather gets cold, seal your doors, basement sashes, and windows with weather stripping (it should have an adhesive back fro easy application).
While many homeowners to remember to clean lint from their exterior dryer vents, they may not realize that common household pests enter the home through this easy-access vent. Examine yours and check that the damper is in good working order - not stuck in the open position or broken. Additionally, ensure that the seal between the wall and the vent itself is secure.
Using latex caulk, fill any gaps between your home's siding and its trim. Smooth the bead down with your finger to seal it. Expanding foam can be used to close any gaps in your soffits. Once the foam has hardened, you can cut off any excess with a knife to create a clean finish.
Glue traps have become popular in the past few years, but they lead to messy and cruel deaths for the rodents. Mousetraps are more efficient - when used correctly. Snap-type mousetraps should be placed in sets of two, parallel to the wall. Mice can jump a single trap, but not two. The traps should be placed wherever you've seen mouse dropping pellets. Bait them with peanut butter or Hershey's syrup.
Your fur baby's food should be stored in either a sealed plastic container (available at big-box stores and pet supply stores) or a metal, lidded trashcan. Mice cannot climb the slippery sides of the can and plastic tubs. To prevent bugs, keep the lid sealed tight. Do not leave pet food in its original bag, on the floor or shelf - it's easy access for creepy crawlers.