This is one of the easiest things you must do in the game, but I still see people mess up on such a simple thing. There is a variety of different ways you can serve, and sometimes you can earn easy points from serves.
On the first serve you take your fingers off of the left and right keys. You don’t have to remove them from the keys; you just have to not press them. You press the up key. That causes you to throw the ball high into the air. Now you have two options. You can stand there and do nothing, yes, nothing. The ball will bounce right off of your forehead, and the ball will most likely fly right over the net. You can also jump in the air before the ball lands. That way the ball would bounce right on top of your hands, causing the ball to soar right over the net. The ball will fly much higher if you jump.