Does he ever do it naturally? Lift a paw to you, that is? If so, reward that right away.
Have you ever used clicker training? Takes a little time to condition the dog to the clicker, but once you do, he can learn anything really fast.
You can search on line for more details, but here's a quick version:
1. Load the clicker. Get yourself a whole bunch of tiny treats (I cut "Pup-R-Oni" sticks into small pieces about the size of a pencil eraser). The treats should be something really, really yummy. Tiny pieces of cheese or hot-dogs also work well.
Get the dog next to you. Click and immediately treat. Do that about 20 times. The idea is that the dog knows that "click" means "treat is coming." Virtually any normal dog will make this connection quickly. To test if he has made the connection, after doing this about 20 times, click and wait a second to give the treat. See if Oliver looks around to see if the treat is coming. If so, he knows.
2. Do a command the dog already knows. "Sit." He sits. Click and treat immediately. Timing is important; ideally you want to click the minute his butt hits the floor for the sit. He learns: aha, particular behavior gets a click and treat.
3. Shaping. You want the dog to lift his paw. Have him sit. (Click and treat). Touch his paw. Click and treat. Lift his paw. Click and treat. Have a hand-signal that you will want him to respond to. (Outstretched hand, maybe?) Do that and see if he lifts his paw. If so, click and treat.
Whatever tiny movement he makes that is in the direction of what you want, click and treat. Gradually you can expect more and more of the right behavior before the click/treat.
After he is responding to the hand signal, add a verbal command - "Paw" or "shake" or whatever you want. Do it together with the hand signal. As he responds, click and treat.
All of this is based on POSITIVE reinforcement. You do not use the word "no." You do not "discipline" in any negative manner. If he does not do what you want, he does not get a treat. That is the only negative consequence for him.
If he does respond with the desired behavior, click and treat.
It works best, for obvious reasons, to do this when he is a little hungry. A few hours after a meal is a good time.
Some dogs are not all that food-oriented, though most are. My Pippin will practically do handstands if he thinks treats are coming; Casey gets more excited if I throw a toy for him to fetch, although he does respond to food treats too. So as you proceed, you might vary the reward from food treats to toys to something else, but always, always, always, a click means a reward is coming.
Google "clicker training for dogs" and you will find a whole bunch of stuff. Karen Pryor is one of the top experts in this area.