This page deals mainly with residential rodent control, for commercial rodent control please follow this link
All trapping efforts are prone to failure, but there are things you can do to make trapping efforts more successful. The biggest reason trapping efforts fail? Rats are very smart, mice are not, and squirrels, are just plain stupid - but they all learn that traps are bad. For rats, all it takes is seeing another rat dead in a trap to convince them that traps are not free food on a big flat stick.
The truth is that even baiting programs can fail - not every rat is going to want to eat compressed bird seed in wax. More about rodent baits here. Maybe they were raised on dog food, or pizza crusts, and whatever you are putting out just cannot compete.
However, there are usually more rats than food sources, so all control efforts stand some chance of success.
There are always more rodents than people think. Never put out one or two traps. Your best bet is to put out 15 or 20 traps in your sub area, the same number in your attic, and at least 6 to 10 in your garage - more, if you see droppings. I routinely put out 30 or more traps per home, and catch 6 to 10 rodents. Understand that the first time you trap - you have your best chance of catching the most amount of rodents. At this point they haven't seen traps - and don't know they mean death. You are most likely to catch the most number of rats within the first 3 to 5 days.
Use the same bait on every trap. The tiniest little smear of peanut butter often works great. DON'T use too much. Spread the traps out at least 5 to 10 feet apart. If you need to do a second trapping there are two things you can do to increase the number of rodents you catch. Use traps that don't look or smell anything like the traps you used the first time & read the last section of this page.
Rats memorize where they go with their whiskers, they run in specific pathways, often along the base of walls or the base of equipment or stored items. When placing your traps put the side where the trap snaps, the short side, which is the 'business end', close to, but not directly against the base of walls or the base of these items. Also place the trap with the trigger in the middle of any area where you can see a 'run way'. The trigger should be in the runway so it can be hit by a rat going in any direction - with the body of the trap outside the runway.
A runway may be where you see a pattern of footsteps in dust, a dark trail of 'rubmarks' showing where the rodents travel, a pattern of droppings in an area, or a depressions noted in blown in insulation where the rats have made trails.
If you need to put a trap in an area that non target animals or children can access it -put in a trap stations or under a milk carton - it might not catch as many things you want to catch - but it wont catch the things you don't want to catch like your kids, wild birds, or your dog.
If you are putting traps out somewhere where slugs can get to the traps, such as outside, or in a damp sub area - use plastic traps that can hold 'in the shell peanuts' they wont rot and slugs wont eat them.
Inspection and exclusion.
Mice can get through a hole the size of a dime, rats can get in through a gap of a half inch or a whole the size of a quarter. If rodents can get back in, they will.
If your home doesn't have rodents in it, exterior rodent control efforts can lower the exterior population by either trapping or poisoning rodents which have never come in contact with those materials. Exterior rodent baiting programs have the most success, since baits work over several days, and rodents have a harder time figuring out what poisoned them. These programs can lower exterior activity - but will not eliminate all exterior activity.
If your home is not rodent proofed, you greatly increase your chances of having rodents move into your home that will not eat rodent baits, and / or that have seen traps in action and will avoid traps. Their offspring - will also be harder to catch or poison.
On the other hand, if your home is rodent proofed, and you put out traps - you are much more likely to cactch them as you will have limited their access to other food sources, and hungry rodents are much more likely to hazard a trap - even when they fear it.