Want to learn a really spinny pendulum serve? Not just a get-the-ball-in-play one that anyone can return, but one with great spin? One with so much spin that the backspin serves will come back into the net and sidespin ones will break sideways as if yanked by a string? Here's how. (The instructions assume you are right-handed; lefties adjust - sorry.)
Step One: Go to YouTube and put "pendulum serve" in the search box. Lots of videos will come up - study them! Study them. You want to have a good idea of what you are aiming to do.
Step Two: Hold the racket out in front of you, forehand side pointing up. (You don't need a table for this.) Toss a ball up, and on the drop spin the bottom of the ball with a right-to-left motion. The ball will jump some to your left. Now tilt your racket slightly so the left side rises (i.e. clockwise). Now repeat, this time contacting the ball on the bottom-left. Now you should be able to spin the ball so that it goes straight up. Catch it and do it again. Do this over and over until you can really spin the ball, and so that it goes straight up. This is how you learn both to spin the ball and to control it. Make sure to just graze the ball - the goal is to make the ball spin. If you do this exercise regularly, pretty soon you be putting tremendous amounts of spin on the ball.
Step Three: Repeat step two, except now go back to spinning the very bottom of the ball. The ball will jump to your left some; catch it. Again, the goal here is to both spin the ball and control it. You need to be able to control how far the ball jumps to your left before you go to the next step.
Step Four: Now you are ready to try this on a table. Repeat step three, except don't catch the ball - let it go. You should now be able to spin the ball and control it, and so should be able to control where it bounces on the table. Practice this until you can spin the ball and control it so it bounces over the net after one bounce, a legal backspin serve. Remember that the contact point is nearly the very bottom of the ball. Don't worry about the height of the serve; focus on great spin and control. When you get good at this, the ball will come to a stop on the far side, and even bounce backwards. Top players can put so much backspin on the ball that it practically jumps back into the net.
Step Five: Now focus on contacting the ball very low to the table, perhaps six inches high, and keeping the ball low to the net. The lower your contact point, and the finer your grazing (i.e. more spin, less speed), the lower it will tend to bounce.
Step Six: Go back to YouTube and again put "pendulum serve" in the search box. Study them! The above is a great way to learn to put backspin on the ball and control it. Now learn to contact the ball with a sideways motion for sidespin-backspin and sidespin. As you get better at it, you'll learn to contact it on the upswing of the pendulum swing for sidespin-topspin. Once you can serve with heavy backspin and control it, it's not that hard to learn the same with other spins.
Step Seven: Now it's time to learn the Reverse Pendulum Serve. As above, start by going to YouTube and put "reverse pendulum serve" in the search box. Repeat the steps above, except now the racket tip points toward you - but otherwise it's exactly the same each step of the way. Good luck!
A few key points to remember: