Haha, I never know what LeeD is talking about, so let him translate it for you. No offense to LeeD, he's pretty cool.
It's already a good serve. Are you sure you are relaxing your right hand wrist at full extension, at the point of contact. If your wrist is relaxed at full extension, the upward direction of your arm will allow your wrist, and effectively, the racquet, to brush up the ball.
If you didn't understand that, think about having your ENTIRE arm as a strand of spaghetti, with the end of the spaghetti being a racquet. Now you throw your spaghetti arm up at the ball. It should be a natural throwing motion. Why does your spaghetti arm keep moving up over the ball after hitting the ball? Because it's loose!
Same thing, keep your wrist loose, and it'll naturally go up over the ball, and, because you're holding the racquet, will have the racquet naturally go up over the ball, too.
At this level, I don't think you should go for a flat serve, intentionally. If you get your serve down, you can bomb every serve, with spin, too. Whenever I hit flat serves, it's usually by accident. I just try to swing fast and hit hard every serve because I'm certain that the looseness of my wrist pronation will allow my racquet to naturally brush up the ball hard every time and have the topspin to bring it down into the court. After you get the looseness and relaxed wrist down, you should go for hard, spinny serves every time.
Also, you might want to straighten your tossing arm. You might get an inconsistent toss if otherwise. You're rushing the trophy pose because of this.
When in trophy pose, try to move your hip up and into the court, like a bow. You'll get a bit more power.