Dogs naturally greet people by jumping up on them but this is an unacceptable, and often times, dangerous behavior. You must teach your dog to sit whenever he greets you or other people. One thing to remember is that jumping up persists because the dog is usually reinforced for doing it. When you give your dog any kind of attention for jumping on you, even negative attention (yelling at him, pushing him off, or even kneeing him in the chest), the behavior will continue. So the best way to stop a dog from jumping up is to remove the reinforcement - your attention.

Jumping up when you enter the house
Approach #1 
When you enter the house and your dog jumps up on you, simply turn your back, stand tall with your arms at your side and say nothing. Watch out of the corner of your eye and as soon as your dog chooses another strategy (four on the floor, or better yet, sitting), turn and give him attention and a food treat. He will most likely jump back up on you and when he does, turn around again and wait. Do this as many times in a row as it takes until the dog sits when you walk in. Practice this exercise repeatedly and then get the entire family involved. Later, invite visitors to the house and have them do the exercise. Keep the treats handy at first until the dog learns that he must sit to greet all humans.

Approach #2 
When you enter the house and your dog jumps up on you, turn right around and go back outside. Wait a moment and then reenter. If the dog jumps up again, leave again. Repeat this process until the dog chooses another strategy, like sitting, when you enter. The dog will learn that when he jumps up on you as you enter, you leave, but if he sits, you give him the attention he wants (and a yummy food treat). Repeat the exercise often until your dog learns to sit every time you enter the house. Practice at each door. Have every member of the family and then some visiting friends practice as well. We want the dog to learn that he must sit to greet all people entering the house.

Jumping up on approaching people
One person should have the dog on lead and tell him to sit while another approaches. If the dog breaks his sit and starts to jump up on the approaching person, he/she should turn around and walk away. Repeat this over and over until the dog remains seated, at which time the approaching person will praise the dog and give him a treat.
Repeat this with as many different people approaching as you can, so that the dog learns that he must sit to greet all people. 
Conditioning a sit at the door when company arrives
Have a helper knock on the door or ring the doorbell. You then coach the dog to a rug located near the door and tell him to “sit”. After 30 seconds give him a treat. Repeat this over and over. The sound of the doorbell or knock soon becomes a cue or command for going to the rug and sitting.