Set your mouse or rat traps in pairs touching but one turned around. If you can find any mouse droppings scatter them around the traps, mice like to go where other mice have been. Peanut butter is good bait so is bacon. Tie the bacon on. If you see mice in the open during daytime then you have rat's who are taking up the best cover and forcing the mice into the open. A little plaster dust on the floor and you can read the footprints.
If you have really small traps bait em with a conservative's heart.