As I was advised by a very experienced person, prevention is better then cure.
I know someone that actually did that, his wife was rather annoyed though, as it was hiding behind her freshly made preserves
Try chocolate
Tiny pieces of Mars bar (and the like) no larger than Petite Poire.
Mouse traps, it depends on the type, those 'gator traps (Plastic kind) are next to useless.
The good old fashioned wooden ones are the best.
As already mentioned if you can get the tip of your little finger in a gap, a mouse will get through it.
Make sure you leave nothing out for it to eat, as above bread crumbs in a toaster,
fruit, crisps, potatoes, cereal etc.
Remember a missed crumb on the floor will feed a family of mice for a week
(OK maybe not, but you get the idea)
Check the cupboard under the sink unit, for droppings,
90% of mice enter this way,pipes up through the floor, generally arent sealed that well.
Same for waste pipes too.
Again as been mentioned, in through air bricks, up the cavity and into the loft.
Check here for droppings also.
Pull up the insulation, to check, particularity around the loft hatch, (warmth) and near the water tank (Moister)
Don't just put your head up there and think its OK
Mice and rats re-act to high pitched noises.
However, those plug in things are a waste of money.
Rodents soon get used to the constant pulsing.
Mouse proofing is pretty much impossible,
but you can help your self by putting fine mesh over air bricks, and checking for tiny holes around the base of the external wall,
particularly if its soil or gravel up against the house.
if its solid concrete, just check for cracks in it.
Professional poisons are about 100x stronger than poisons "over the counter"
and all you are doing is feeding them with it.
Of course there is a risk with something dying inside if its poisoned.
If you do put put poison down, and you find an entry point,
what ever you do DO NOT block these until you are satisfied that everyting is dead.
Poisons, 2nd / 3rd generation anti-coagulants, have a dehydrating effect,
inasmuch as it make the target species very thirsty, and they head for water, usually the way they
came in.
If their escape route is blocked they will die in walls, under suspended floors etc.