I remember going to a dog park where a little 4-month-old Boxer puppy ran around jumping on everyone. The dog was not heavy enough to knock most of the adults down. However, it left everyone with muddy pants and the dog was big enough to knock over small children. The owner did nothing to stop the jumping puppy. After all, it was just a small pup. Everyone around her was pretty annoyed at the muddy prints the dog was leaving all over their clothes. That is an owner who will have a problem with her dog jumping on people when it gets older.
Other commands can be substituted for ‘sit’ if you prefer, such as ‘stay’ or ‘down.’ However, if your dog simply gets too excited to execute these commands properly (as is often the case, especially with puppies) try diverting their attention elsewhere. Ask them to go find their ball, or a favorite toy, as a way to distract them and expend some energy. And, as always, reward the good behavior with praise.
While the idea of "training" may seem daunting, it is simply teaching an animal what behavior works or doesn't work through resulting consequences — so whether you realize it or not, you are actually training your dog every moment of the day. Fortunately for you, preventing jumping is possible even without structured training. There are some simple solutions to this problem that require minimal effort and fit easily into your normal interactions with your dog.
When a dog jumps on a human of its own free will, it is not "greeting" the human, it is asserting its dominance over the human; it is the dog communicating that it is alpha and/or wishes to own/control the human. A subordinate would never dream of running over and jumping on the alpha dog of the pack. Space is respect and lower members of the pack respect the higher members. If your dog jumps on humans, it does not respect them. Note: when a young puppy jumps on humans it is sometimes its attempt to reach one's face. Puppies need to be taught not to jump up on humans as this behavior will manifest into other meanings as the puppy grows up into an adult dog.