You have decided it is time to get a puppy. Like most everyone else you dream of a dog who is non reactive, you can take them anywhere and they will behave. Now how do you achieve that? Well, if you are going the route of a breeder, be sure to ask the right questions. Have the puppies had exposure to strangers? How many stranger interactions have they had? 5,10, 30. 100? The more the better! Have they been exposed to a variety of different types of people? Tall, short, male, female, children? What sort of surfaces have they had exposure to? Wood flooring? Carpet? Grass? What about Stairs? Do you do a puppy culture type environment for them? What about exposure to loud noises? These first weeks of a puppy's life are crucial to begin forming a positive relationship with as many things as possible that they will encounter in life. If the window of opportunity is missed, a dog will never meet it's full potential. Now, I am not saying that the dog can not lead a full, happy life. I am not saying you can not form positive experiences past this first weeks and months. What I am saying is this. If you take a pup/dog who is fearful or nervous and spend the time required to properly counter condition to the dog's triggers and now have a dog who is no longer fearful of something but instead defers to you for guidance, that dog still has an underlying predisposition to be nervous or fearful. It is unlikely the dog will ever be 'bomb proof' so to speak. This is not to say your dog will not become more confident in themselves, or become a working dog even.
If you are bringing home a puppy, who may or may not have had early exposure, it is your job to now ensure that exposure either starts or continues. Your 8/10 and even 12 week old puppy can safely be exposed to the world in a variety of ways. Carry them, put them in a wagon or simply go for a drive. If you have pet friendly stores near you, toss a blanket in the bottom of the shopping cart and take a trip around the store. Always keep in mind that a pup this age is not fully vaccinated so keep those paws off the ground unless at home or in a safe and enclosed yard. Safe and early exposure is the key to a well balanced and no reactive dog.
Now, if you are past the point of all of this and you have a reactive dog, please reach out to myself or a trainer near you for behavior modification training. It is not too late to improve or even change the situation. Counter conditioning works. It just takes time, patience, and dedication.