This command is very easy to teach and quite a popular one as well.
STEP 1. Place your dog into a sitting position directly in front of you. Give the command "Shake".
STEP 2. Gently take his paw and give it a pump or two.
STEP 3. Reward with a treat and some good praise.
(Your dog will start to catch on that you're going to shake his paw when you say "shake". Once he gets this,
he will start to anticipate your handshake and lift his paw on his own. Give better praise when this happens.)