Teaching a dog not to jump up on people can be difficult. Well-meaning friends who say, "It's ok, I don't mind" and pet him for jumping make it even harder. But, where there is a will, there is a way.
Relationship based training philosophy

Actually, there are several ways to teach not jumping. You will find that some work better with certain dogs, and others work better for other dogs. The constant for all dogs is that he should NEVER be rewarded for jumping up. If you occasionally give in and pet him when he jumps on you because you don't really mind in that moment, you will make your task nearly impossible. It works on the same principle as gambling. The fact that people win only occasionally is what makes them keep playing. Even though they lose most times, they keep playing for the time that they will win. For dogs, the thought is 'I didn't get the attention I wanted from jumping up this time, but I'm sure to win sooner or later". It's also a good idea that you don't punish the dog for jumping. Jumping is a friendly act from the dog's point of view. Punishing it may cause the wires to get crossed between what you are trying to teach and what they learn, and your dog could learn to NOT be friendly with people!

The best offense is a good defense. An ounce of prevention is worth a pound of cure. The early bird gets the worm. Ok, one of those doesn't really apply here. The point is that it's easier to keep them from learning the habit in the first place than it is to break the habit later. Don't let your puppy jump up on people if you don't want him to jump up on people when he's an adult.

Stop the jump before it starts. IF you see your dog thinking about jumping up on you, hold your hands in front of him, palms facing him, in the universal "STOP" signal. Take a step back if necessary. This usually stops the jump in its tracks. Take that moment to redirect his attention to something else, or kneel down and pet and praise him for not jumping.

Cross your arms (so he can't grab your hands), and turn your head away, ignoring the dog. Jumping is an attention-seeking behavior. Turning away your attention will discourage your dog from jumping. As soon as he settles down, turn your attention back to him and praise for getting it right!

Be proactive. Teach your dog something more appropriate to do when he wants attention from you or a visitor. For example, you may wish to teach him to Sit when someone comes to visit and wait for them to pet him. Always pet and praise for this to make it worth his while!

Additional Resources

Teaching your dog not to jump

Jumping up on people