How much to feed :

Follow the guidelines on the package of food.
Adjust the actual quantities according to:

age

temperament

environment

activity level

NOTE: Plenty of fresh water at all times.

When to feed :     

Feed at regular times per day.

Puppies less than six months old should be fed three times a day.

When they are older only two feedings will be neccessary

Adjust feeding schedule around times of heavy exercise

Feeding to close to a bout of exercise may lead to bloating

Changing food :     

Switching food may cause a bad case of diarrhea with your dog.
To prevent this follow a ten day plan:

Day 1:
Put 1 part of new food with 9 parts of old food.

Day 2:
Add another one part of new food and reduce the old food by one.

Day 3 to 10:
Continue this trend until the dog is feeding only on new food.