Here are some tips to help you:
After a bad point, take a step back from the ping-pong table, and take a deep breath. If you are upset from the last point, it will do no good wasting the next point because you are mad. Don’t get mad about the last point, you can not change what happened, so let it go!
If it is your serve, take your time to get back to a good mind set.
And finally, try not to let it get to you in the first place. I believe Joseph Redding said it the best when he said, “IT’S JUST PING-PONG”, winning isn’t everything, but character is.