Teething is the most critical time. Anything you teach the pup during teething will be relate to pain. Teething usually lasts until 4-5 months of age. Check pup's bite daily to see that baby teeth are coming out. Crate training is ideal.
Puppies play hard but sleep long hours.
A crate represents a den-like safe place. It also helps in house training. Place your crate where pup can see you - beside your bed at night is ideal. This gives the feeling he is not alone. Dogs are pack and social animals.