Rats are cautious, and it may be a week before they approach a trap. Mice are curious and will normally approach traps the first night. If you don't catch a mouse in the first few nights, the trap is in the wrong location. To help rats overcome trap shyness, place traps unset, in place, for several days. This allows rats to overcome shyness and results in better catches.
Baited traps rely on the rat's being attracted for feeding.
The bait must compete with other available foods, so no one bait is ever the best bait for all locations. Rodents living on garbage or spoiled food prefer something fresh. Raisins or grapes for roof rats. Sardines packed in oil for Norway rats. Dry rolled oatmeal is excellent for mice.