Pendulum serves

For the Pendulum serve, concentrate onthe contact for a little while.  Make sure you are brushing the ball on contact.  If you are still finding it difficult, go back a step and see if you are getting spin when you try to spin the ball on the floor.  Then take it back to the table and try again.

For the reverse Pendulum, if the ball is going into the net, you may be hitting the ball from too low and similarly with the serves going too high, you may be contacting the ball when it is too high.  This is not an easy skill to master.  Now that you have the basics spend as much time as you can practicing it so that you can get th etouch to do it consistently.

The serve si certainly allowed to bounce more than once on the opponents side.  In fact, that is what you should be doing to improve your serve.