One of my favourite quotes is by Dr Ed Bailey, regarding behaviour problems in dogs. It matches my philosophy perfectly.
"Behaviour problems avoided are problems that don't need to be fixed. In the case of dogs, most behaviour problems are created, or at least abetted initially by choice of "parents" and more often by mistakes made during the pup's first 12 weeks of life".
It is incredibly important to recognise how important the first 12 weeks of a puppy's life are and treat them as such! The first 3 months of a puppy's life is a huge responsibility and will contribute much to the behaviour of the adult dog.