The grip: grab your racket in a continental grip, but orient it slightly more vertically. So, if you stretch your arm out vertically, your racket should point straight up to the sky.
Tossing the ball: you want to toss the ball so that it floats straight up and straight down. Don't let the ball travel too far towards or away from the body.
Contacting the ball: you want to contact the ball towards the top of the face of the racket, and you want to come down on the ball at an angle in order to keep it from landing out of the service box.
Putting it all together: at this point, bend the knees, toss the ball, and serve the ball, making sure to follow through to the opposite side of your body.