What should I consider before adopting or buying a puppy?

I think the most important thing to consider is what breed of dog you're looking to get. And to be even more clear about that, what kind of dog is going to fit into your lifestyle? With some people, it's quite easy. Maybe you're a duck hunter and you know, hey, I want a Labrador Retriever and you know exactly what they're all about and how they work and their drive and that's great. But a lot of people tend to make the mistake of wanting a puppy because they're cute, especially when they're a puppy.
What I would implore you to do is look into the history of what that breed was, I don't want to say created for. If you live in a one or two bedroom apartment, a Border Collie or a Blue Heeler is probably not going to be the breed for you. They're very high-energy working-type dogs. They need a job to do. If you don't give them a job, they are more than happy to make their job eating your sofa or your carpet or they're going to find something to do with all that energy they have and it may not be to your liking. 
So my best advice is plan ahead, look into the history of the breed, their temperament, their energy level, all those things, and make sure you're picking a breed that fits not only what they look like. That part is easy but you want to pick a breed that fits your lifestyle and what's going to mold best into your lifestyle.

You want to consider the breeds you are interested in and how they match your lifestyle. So, in the case of an energetic breed, make sure that your lifestyle is pretty active. Because if you have a more sedate-type lifestyle, you may be in for a rude awakening as far as how much energy your puppy has.