3 Ways I Improved my first serve

First focus on tossing in-line with the net post; this will give you the accurate direction in your toss which will let you stop making to many faults

Rather than being tight and trying to go for a 140 mph bomb. Instead try to be very loose on the take back and just swing it more freely for easy power

Hit with your legs and watch your serve get an additional 10 miles. Using forward momentum will help you increase your weight on your shot and increase your power.