Remember, Jumping up can be dangerous as well as annoying. Just as many owners are sued for their jumping dogs as their biting dogs. Young children and elderly people can easily be toppled over and seriously injured by exuberant, friendly dogs. Start now to teach your puppy not to jump up. Even little dogs can cause problems and injury to themselves and others when they jump up.
When he gives up and stands still (staring at you like you’ve gone crazy), THAT’s when you greet your dog and give him some love and attention. This is the reward he was looking for. Following these rules will ensure he learns that he will only earn that reward by not jumping (don’t overdo the high-pitched voice saying, “GOOD BOYYYYY” or it will just rile your dog up even more to start jumping again).
You shouldn’t stop this type of jumping. You need to diagnose your dog's issue and remedy that. If your dog is just stressed being in a new situation, you should calmly get them off of you, offer them a treat to calm them down, and have them sit politely beside you until their stress level has subsided (or take them somewhere else so that they can calm down if it is taking a while for them to calm down.) But most of all, please do not just ignore this behavior change.
Also, it's your job to never let anyone else allow your puppy to jump up on them! They will say, "It's OK, she's just a puppy, I don't mind if she jumps on me". You must rush in and pull the puppy down immediately, put your pup in a sit, praise the puppy then scold the person ! Continue to hold the puppy in a sit and let the person greet the pup. Explain to them they can never allow the puppy to jump on them - the puppy must sit to be greeted. To stop the jumping up behavior in pups, I do as much people training as puppy training!
Start by teaching your puppy the word NO. Use that word only when she is doing something you do not like. You have to use the word NO in a loud, stern voice that is different from all other ways you communicate with her, so that she knows there is something wrong. You also have to catch her in the act that you don't like, so that it will associate the word NO with the action that she is doing. Be consistent, and follow your verbal command with a light smack or moving her to a time out spot.
Unless given a command to jump, a dog should never be allowed to jump on humans. A dog that jumps on humans of its own free will is a dog that does not respect the person it is jumping on. Even those cute little toy dogs should not be allowed to jump on people. While you may think it is cute, it is not cute to everyone else. Not only is it annoying to most people to have someone else's dog jump on them, it can also be dangerous. A jumping dog can knock people over, muddy their clothes, put runners in nylons and scratch the skin.