The main thing is to make sure there is no access to food. Keep everything in high cupboards/tins/plastic boxes. No fruit out, hoover/sweep/mop all areas where food is eaten daily. Any food you might leave out - even bread in a bread bin - they will smell and come for a look. Where there is no food source, there will be no mice - they don't travel far from home for food.
Block holes with wire wool and polyfilla/specialist rodent hole blocking compound. Don't bother with expanding foam - it's porous, they smell food through it and they can chew through it too.
Mice can squeeze through the tiniest of holes - don't assume a gap is too narrow. If you can poke a pencil through it, a mouse can get through.
Spray disinfectant and peppermint oil can act as a deterent, but the plug in mouse repellers are only of use if the mouse is within ear shot of the thing - the noise the repellers make doesn't travel through walls or furniture.
Snap traps are the most humane way to deal with mice - humane traps are all well and good but where are you going to release the mouse? If it's in a field, it will die a gruesome outdoor death and if it's near someone's house you're giving them the problem. Poison will kill a mouse slowly and painfully, and other animals will eat it and get a dose of the poison themselves. And while that might sound like a 'two birds one stone' solution, what if the dead, poisoned mouse is nibbled by a pet cat or dog? Also, a dead, rotting mouse in the walls will stink your house out till it's totally decomposed. And glue traps are just cruel.
If chocolate and peanut butter don't work in a snap or other type of trap, try dry cereal or butter. Not all mice go for the same snacks, picky buggers.