I prefer to think of it in terms of the axis of spin I'm trying to generate and then work backwards to swing path and racket face angle at the instant of contact and then overall swing path to execute.
So if you want 6-12 topspin, what racket face angle and swing path at the instant of contact? If you want 9-3 slice, what racket face angle and swing path at the instant of contact? If you want something in between?
Now, how do you get there within the constraints of a high level serving motion?