Having a dog that jumps up on people is not only irritating, but it is also embarrassing and potentially dangerous. Especially if the one being jumped on is a small child.
When a dog jumps up on people, it's their way of saying, "hi". I think it's more bound to happen with children, because of their shorter stature. Basically your dog is saying, "Notice me!"
Before you can teach your dog not to jump on people, they should already know the "sit" command. If your dog does not know how to sit, here's a quick easy way to teach them.
You will need one of your dog's favorite trips. Get your dog's attention by calling their name. Once you have their attention, make sure you have eye contact as well. Let your dog see the treat and smell it inside your closed fist. Gradually move the treat from his nose toward the back of their head. As the dog lifts it's head trying to follow the treat, they will automatically go into the sit position. Now immediately give them praise as you give them the treat. Continue this a few times, saying the command, "sit". Your dog should have this mastered in no time.
Now on to the jump on people. The first time you have company over and your dog is ready to jump on them, immediately tell the in a firm voice '"SIT!" This will prevent your dog from jumping up. After all, it's hard for them to jump when their in the "sit" position.
If this does not work, have your company IGNORE your dog and even turn their back on them if they have to. When the dog is calm and not jumping, now your company can acknowledge them. You can now also give them praise and give them a treat. This tip works pretty well as you're keeping your dog for good behavior rather than scolding them for bad behavior.
This method was used on my young female lab and it worked terrific. She now sits and waits to be petted when company comes over.