Why does my dog keep jumping up at people?

Ideally, the answer is to set the ground rules from the very beginning - no jumping up, without exception. The best way to achieve this is to teach your dog that it will not receive any attention until it sits. The theory being that a dog cannot sit and jump up at the same time.

Whenever you arrive home, request your dog to sit. Completely ignore them until they do so. If they jump up, turn your back and ignore them. Don't speak or give them any attention, just keep requesting your dog to sit. The minute they do sit, heap warm praise on them. If they start jumping up again, go back through the routine of ignoring them and requesting them to sit. Practice this with yourself and your family, ensuring everyone applies the exact same routine, with out exception. Your dog will quickly realise, it will only get attention when it sits.

When you get visitors, ask them to do the same and give them a treat that they can give your dog the second it sits. This will raise eyebrows from some visitors, but it is important that your dog has good greeting manners with all people, not just you and your family.