Does your dog jump up on everyone who comes through the door? Is he driving your guests crazy with his incessant jumping? This type of behavior is relatively normal as it is one of the most common ways in which dogs show their joy and affection to people they know. Basically, it is his way of saying "hello" and at the same time "pay some attention to me". Unfortunately, not everyone appreciates your dog's enthusiasm.
Chances are good that while your dog was a puppy, you reinforced this type of behavior. Puppies are so cute and little that their enthusiasm seems harmless. In most cases, it only becomes a problem when the dog becomes big enough to cause injury to the person he is jumping on or knocks things out of their hands.
Most people tend to use a voice command such as "down", "off", or "no" to bring this kind of behavior to a grinding halt. You can create your own command if it works better for you, but remember to use the same command each time so that your dog does not get confused and knows exactly what is expected of him each time.
You should wait until your dog is old enough to have mastered basic behavior commands like 'sit', 'stay', 'come', and 'lie down' before you attempt to teach him to stay down. The reason for this has more to do with age than anything because your dog will have already started to calm down by the time he is old enough to have mastered the basics. Of course, be sure to have plenty of his favorite treats on hand to reward him for getting things right.
Teaching your dog not to jump on guests will take plenty of time and patience, as well as a healthy supply of his favorite munchies. You will need an assistant, preferably one of your dog's favorite humans, or if you can gather several friends together this can make the training go more smoothly and quickly, depending on the training method you choose.
One of the most important things to keep in mind is that you must always use the same command and give in a voice that lets your dog know you mean business. If you allow him to think otherwise, he will not see you as alpha and is never going to obey you. It is your job to convince him you are the alpha dog in the pack.