Before making the serve, hide the ball in a way that your opponent cannot see it. For that purpose, you can use your body as a shield and your opponent will not be able to see when you drop the ball. Use this technique especially when you are planning to make a hard serve.
When making the serve, you should stand in a way that you can create some visual obstruction to your opponent.
For that purpose, you can make a stance that is perpendicular to your opponent.
Make a serve in a way that the ball should drop next to your front foot. This will fall out of your opponent’s field of vision, for a split second.
When making the serve, consider hitting the ball when it is slightly ahead of you and change the angle of the racquet just before you hit the ball. This way, your opponent will be disguised, if he or she had an eye on your stance and racquet before you made the shot.
Before you make a serve, you can also alter your step. This will help in changing the direction of the ball.
So, you can make variations in making long and short steps, and disguise your opponent completely.