1) Set your own tempo and rhythm.
You need to always serve at your own tempo and pace.
Never allow your opponent to dictate the tempo on your service games.
2) Start your motion on your own terms.
Never start serving until you have mentally recovered from the last point.
If you feel any carryover effect.
Step away from the baseline and breathe deeply for 3 times and start your pre-serve routine again.
This will help you set and maintain a good rhythm for your service games.
3) Never rush through your motion.
This is a very important point when serving.
You should never feel like you are rushing before or during your service motion.
Your body needs to be relaxed and your mind should be picturing one fluid service motion.
Again, if you are feeling nervous at any time before you start your service motion.
Step away from the line and repeat the above suggestions I just gave YOU.
Then start your pre-service routine over again.
At the junior level.