New parents are often amazed at just how often a puppy has to go to the bathroom. Often!! My puppies are bigger than little mini puppies and have bigger bladders, they can last a bit longer however, when they are running and playing in the kitchen they can have to go pee once every hour or so.
When you take puppy out it is likely he will go to the bathroom fairly soon after he feels the nice absorbent grass under his little feet.
Praise puppy as soon as he pees so he knows he has done the right thing.
I notice that in this house it is easy to forget a puppy playing in the corner and Jean sets a timer on the oven so that she remembers to take the puppy outside.
Don't be upset when he goes to the bathroom under the table or in the corner. He really doesn't know what he has done wrong but thinks to himself "gee...peeing couldn't be good". Then he will slip away and try to pee when you are not looking...maybe behind the sofa.
Our friend read in a book that when a puppy pees in the house take a rolled up newspaper and hit yourself over the head with it. I thought that was pretty funny.