Detection training is normally applied to specific breeds.  For example, blood hounds are typically sought for finding people because of their hyper sensitive noses, which are ten times more sensitive than most dogs, while K-9s are more often used as drug dogs.     Sniffing dogs are trained using generally the same principles as most service dogs with some key differences according to the type of service they will perform and dependent on the desired results.  It is also important to note what qualifications are necessary in order to certify to work as a drug dog in the local law enforcement.  All this said, here is a simplified and summarized guide at training your dog at home.

Training a drug dog is relatively similar to training a dog to perform any other skills like sitting, fetching or staying.  The key is to drill with repetition and association.  When performing tasks, you praise desired behavior and punish undesired behavior.

A common drill used by trainers employs to use of a set of boxes.  Start with 4 and gradually increase each time until your dog is able to concentrate with 8.  

Prepare the boxes for the drill by cutting holes out in the tops of each box, measuring about 3-inches in diameter. 

Designate one of these boxes as "hot box".  The training aid should always be placed in the same box, in order to prevent contamination.  Dogs are great at sniffing out drugs because of their sense of smell and if you change the box containing the aid, the smell with linger on all the boxes, whether the aid is there or not. 

Set the boxes up in a row and have your dog sniff each box.  When your dog gets to the hot box, allow the dog to smell the box and then give him a “tell”, which is commanding him to sit in front of the correct box.  If he obeys this command, reward him.

If your dog does not obey, you will need to correct him.  A correction should not come in the form of beating or screaming.  You can correct by a stern verbal command like “No” or a gentle tug on his leash.  

Repeat the drill several times each practice session by switching the order of the boxes.  You’ll need to switch the box order in order to prevent your dog from associating and memorizing based on the position of the boxes. 

You’ll have to repeat this process many times for several weeks (all dogs are different) in order to train your dog to alert to the scent that signals a reward.  

Eventually you’ll want to get rid of the tell - signaling him to sit at the correct box - and allow him to figure out the steps that lead to a reward.  As time goes by, the dog will associate finding particular scent and sitting with getting a reward. 

Once your dog has mastered the box drill, you’ll want to proceed to the next level.  Introduce him to new environments that are still in his comfort zone.  Hide training aids in places he is still familiar with, but beyond the line of boxes.  Good options for this step would be vehicles, luggage, under couches or in closets.

Once he’s mastered this, you’ll want to introduce him to an even broader range of exercises and environments.  Now you’ll want to take him out of his comfort zone and into unfamiliar places.  Hide training aids in other buildings and in large, open-spaces, like parks or beaches.  Expose the dog to as many different situations so that when it comes time to real work, he’ll be knowledgeable and comfortable in all settings. 

In order to be a certified drug dog, your dog and you or his handler must pass a certification test separately and together.  In general, no handler is permitted to work with a dog that s/he has not been certified with.

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