If you’re a beginner, you can start with an eastern grip or simply by shaking hands with the racket. That’s fine. Eventually, you’ll need to switch to a continental grip to enable spin variation.
Regardless, you should position yourself sideways with your foot slightly pointing forward. Avoid being completely sideways with your foot pointing forward and my racket pointing in the direction where I want to serve using my non-hitting hand. Keep it slightly above.
To serve in tennis, there are two motions: tossing and swinging the racket. Begin with the backswing, where you let your arms fall and separate while tossing the ball. Ensure the ball is tossed higher than the height you reach with the racket.
To achieve a proper toss, ensure a high trajectory while aiming sideways at the target. Begin by lowering your arms. Release the ball and observe the resulting position of my racket, pointing upwards. This arm indicates the direction of the ball. How can I be certain? It is because I have executed a successful toss.
If I throw it higher than my racket in that manner, and if the ball approaches near my hand at the end of the throw, then throw it like that. That is a favorable throw. If I have to extend my reach in that manner, then it is an unfavorable throw. Therefore, it is necessary to practice allowing the arms to descend, releasing the ball at a sufficient height and in the correct position for striking.