Unlockable Dogs (Japanese Version):
Toy Poodle - Collect 4000 Owner Points
Jack Russel Terrier - While on a walk, your dog may come across an Item called the Jack Russel Book. If you visit the kennel, you can now buy the single Jack Russel Terrier
Shetland Sheepdog - Collect 17000 Owner Points
Cavalier king Charles Spaniel - Collect 14000 Owner Points
Welsh Corgi - Collect 10000 Owner Points
Shih-Tzu - Collect 8000 Owner Points
Beagle - Collect 2000 Owner Points

Unlockable Dogs (US Version):
Yorkie - Collect 2000 Trainer Points
Jack Russel Terrier - While you walk the dog, your puppy may find a rare present with a "Jack Russel Book" inside. Visit the kennel, you can now buy a Jack Russel Terrier.
Dalmatian - While you walk the dog, your puppy may find a rare present with a "Firemans Hat" inside. Visit the kennel, you can now buy a Dalmatian.
Shiba Inu - Collect 4000 Trainer Points
Cavalier K.C. Spaniel - Collect 8000 Trainer Points
Pembroke Welsh Corgi - Collect 10,000 Trainer Points
Shetland Sheepdog - Collect 14,000 Trainer Points
Miniature Schnauzer - Collect 16,000 Trainer Points
Boxer - Collect 20,000 Trainer Points
Toy Poodle - Collect 22,000 Trainer Points
Chihuhua - Collect 45,000 Trainer Points
Miniture Pinscher - 35,000 Trainer Points
Lab. Retrieiver - 50,000 Trainer Points
German Shepherd - 30,000 Trainer points

Unlockable Rooms (US Version):
Desktop - Collect 6000 Trainer Points
Seaside - Collect 12,000 Trainer Points
Outer Space - Collect 18,000 Trainer Points
Northern European - Collect 25,000 Trainer Points
Urban Living - get 40,000 trainer points

Eat A Lightbulb:
When your dog performs a trick in the game a lightbulb will appear. Click and drag this lightbulb to your dog and he will eat it. You can also eat bones that appear above your dog as well.

Easy way to prevent yourself from passing un-marked ?-Boxes on walks:
Sometimes when you're on a walk, you'll notice a present go across the screen at seemingly random times, and there's a chance you won't get it because you weren't paying attention. To prevent this, simply watch the map on the upper screen.

Whenever your dog stops moving on the map, it will either stop to go to the bathroom, or sniff at a spot it previously went to the bathroom at. However, sometimes the dog will not stop on the lower screen, which means that something that isn't marked on the map is about to appear. It will either be some garbage, or an unmarked ?-Box is about to appear.

Basically, if the dog stops moving on the map, but is still moving on the touch-screen, get ready to tug at the dog's leash so that you can pick it up.

Get unlockable breeds easier:
Do Bark Mode with a dog in a breed that you don't have.

Example: Do Bark Mode with a Chihuahua and after you do Bark Mode with that dog, you will be able to buy the Chihuahua breed at the kennel.

NOTE: This only works the first time with each different version of the game. So you can do this trick one time with Labrador & Friends, Chihuahua & Friends, and any other version of Nintendogs.