I used to practice my serve daily. But then I learned that by serving daily I wasn't helping my serve a lot because I was actually practicing bad technique so by practicing bad technique often you don't get better. You just get consistant at hitting the ball badly.
Most of my improvement on my serve came from off court drilling. Improving my toss, catching the ball against the fence, throwing with my arms.
Beginners worry about head racquet speed too often and forget about technique and their toss.
Advanced players developed good fundementals but are now trying to improve head racquet speed, thrust, rotation, while they could still develop more into their fundementals.
I think at most levels improving your fundementals is more important than focusing on power, pace, spin, or technique even. Even if you have excellent technique and you chase a bad toss, your serve can often go out.